My opinion is very biased as everyone here knows, I am a fan of Russian equipment and not so much of a fan of western equipment.
I am also pro Iran in current affairs... not because I am a muslim, but because they are clearly being bullied, for reasons that are either not clear or not their fault.
When you boil it all down their major crime is to support the people Israel is victimising in its land grab, and to be honest I support them supporting those people too.
In comparison a few countries in the region and the ones doing the bullying have done much worse and have supported some terrible groups who have done terrible things around the world, so as an excuse to punish 60 million people it is just not valid.
I agree that their ballistic missile programmes seem well worth the money... long and intermediate range..., and UAVs and UCAVs would be very useful too as force multipliers for ground and air and naval forces... all the assistance of air power but with reduced costs and overheads, though not actually replacing air power when the real stuff is needed. Iran has licence produced a lot of products and should keep looking for products that they can make that will be useful for their defence. A bit of cooperation with the countries you mention should boost their potential and allow improvements in both directions... (Projects with India and China and the UAE and Jordan have improved Russian products considerably... simply having a third party demanding better and funding those upgrades means the equipment produced is better and more capable without going silly. For instance the Pantsir could have active radar homing missile seekers in each missile... they have the technology... but that would make it a rather more expensive system to use while not improving performance that much... a tiny radar like that would not be that amazing until it got very close to the target... so it would be better for a tiny fraction of a second than the much bigger radar on the vehicle because of the very high speed of the missile but it would make the system horrendously expensive to actually launch missiles from...
Regarding the Kowsar, Russia is introducing external pods for aircraft to improve air to air or air to ground performance so such targeting pods would be fantastic for light cheap aircraft to boost their performance in certain areas without making the aircraft super expensive... for instance if the target is drones then an air to air targeting pod perhaps combining MMW radar as used on Russian attack helicopters to detect and engage the drones with a thermal sight and digital day/night vision device for identification... and racks for MANPADS weapons or even cannon pods with air burst shells. If the light aircraft is going to come up against enemy aircraft a datalink with ground based air defence... perhaps in a pod to start with... and built in later on, and a self defence EW pod from Belarus with a rack of AAMs hanging underneath it...
An aircraft redesign so the pods can be mounted conformally to the body of the aircraft so the wing pylons are free for ordinance or external fuel... because the F-5 was always a light fighter, it would be easier to convert it into a modern light fighter...
Perhaps spend some money with a Russian fighter company and explore options of new wing shapes to improve performance and allow heavier operating weights and more fuel or equipment being fitted into a larger heavier wing for example. A thicker profile wing won't reduce flight speed too much but could shorten take off and landing runs and increase internal fuel volume without filling up the planes internal spaces and just add lift force. Larger control surfaces could improve handling if that is a problem... it is hard to offer advice without knowing what their experience is with this equipment.
The Su-22 was a solid aircraft and there would be a lot of ways to keep it useful.
The Il-76 would be ideal for Iran, it is an excellent aircraft and a solid performer with newer models getting better and better... (I think we should have them here in NZ but no politically acceptable... we have to have Hercs that can barely reach Australia from New Zealand with a full load... so anywhere we go requires lots of hops. Not being pressurised means you fly through the weather instead of over it... an Il-76 can carry more than twice as much over much greater distances much faster... and they are cheaper to buy than new model C-130s.... and with the same payload weight... say 15 tons they could probably both operate from the same grass airfields... but the Il-76 could fly much much further with it.)
Buy TVS-2DTS (AN-2 replacement) buy production and/or parts. (not sure if Iran is still getting knockdown kits from Ukraine on the AN-140 but at least this would give Iran some form of light transport)
Not familiar with how up to date Iran is with composite materials but this would be a good place to improve their skills... the goal is to make a light capable aircraft as cheap to operate as possible so it can be operated out in the middle of no where without needing highly technical and expensive support... if it can do that then it will be ideal for lots of smaller countries and outback regions of bigger ones...
I would think a strike version of the Su-30 would be a better idea... would be capable and I think many deep strike missions would be better executed with ballistic missiles or cruise missiles or drones rather than manned aircraft...
The range of stuff they could buy is enormous, but the list of stuff they want to buy or will buy will be shorter and will be broken down by priority because they wont be able to do all this at once.
I would see all this as an enormous boost to Iran, but an Iranian might see it as an enormous investment risk... it is important to keep clear Iran and Russia are rational and sensible countries, but they are not best buddies. For whatever reason the Russians delayed delivering of previously ordered S-300 systems to Iran which Iran could see as a betrayal even though they got the systems and those systems should make a serious positive difference for Irans self defence, there is that issue which ruins the gesture. At about that time there was talk of Saudi Arabia buying billions of dollars of new Russian equipment like S-400 and Iskander etc etc which never did eventuate which suggests such promises were made to influence Russia and when it became clear they would not be more than promises the sale went ahead.
Fair enough for Iran to say Russia is not reliable.
But Russia could equally point out that all the international hostility and pressure is coming from the west in general and the US in particular and when Iranian funds were freed up Iran started ordering Boeings, so why would Russia trust Iran? They are clearly mad.
It might be a secret agreement regarding the release of the Iranian funds that they spend a percentage on US products for them to be released... which would be just the sort of thing the Americans would do of course, but how can Iran blame Russia for what they did when Iran is influenced too.
The facts are that Russia and China have a variety of weapons and equipment that would be useful to Iran and both countries probably would have no problems selling to Iran. Can't really say the same about anyone else because any other seller is likely to have the sky dropped on them by the US and her cronies, while Russia and China are like Atlas and are holding up the sky anyway... so no difference.
Russia lost eastern europe as a market so Iran would be a useful addition to countries they can openly trade with and I am sure with recent diversification of the Russian economy that Iran would benefit from trading with them too. The Caspian Sea would be the ideal way to ship goods that the west/US cannot interfere with in both directions.
Now this does not mean Russia and Iran are best buddies and that Russia will defend everything Iran does nor that Iran needs to back Russia up with everything too. This is a trade relationship... Russia wont use this to demand cultural or religious or any other changes in Iran and Iran cannot expect Russia to change culturally or religiously or in any other way. Fair trade. Business and development with both countries improving and developing with no interference in either direction. The polar opposite of what the colonial west offers...