A fleet of 60 Su-35 would act as a catalyst for Irans IADS. At that number, real added value.With the now in service Khordad 15, Third of Khordad, Bavar-373 and a slew of AD/SHORAD systems: where exactly does Iran stand in a fight against regional powers? -- emphasis being on possible conflict the U.S. military.
I think we can safely say that Iran absolutely does not plan on building any sort of near-pear or even adjacent symmetrical Air force capability that rivals its neighbors toe-to-toe due to cost and the looming threat of obliteration from newer generation HGVs and the like. Iran acquiring a smaller amount of modern air-craft that are multi-role and can fulfill certain defense/offense requirements without straining the national defense budget is in my view an absolute must.
The Aerospace missile force still caries Iran's primary means of attacking back and has proven itself (at least somewhat) to be an effective method of attack in practice although the tactical viability of the force still is in question due there not being a active conflict to test them out in full.
We can only wait and see on how Iran wants to move forward regarding it air-power. Honestly I would be okay with a small acquisition of some sort of Multi-role air-craft.
A fleet of 250 Su-57 would only drain money from missile and air defense projects.
A fleet of 300 5th Gen. Iranian fighters built from 2030-2040 could be justified and create a expeditionary force capability for Iran as well as advance the overall industry.