@VEVAK
You are right that getting such a CAS fleet is a luxury thing for Iran as it has a enemy that can more or less stop their safe operation. But what if Iran is at a stage where it can afford this luxury? You gave the answer: Border guards, insurgencies in or outside the borders, in such low intensity warfare this capability is very welcome and we could not effectively provide it to Syria and Iraq in the past.
So are F-4 or Su-24 like the Russians uses better than a F-5? No. These are aircraft capable of interdiction strikes. You have more capability than you need and must pay for it with very sortie. Mach 2 capability, swing wing (Su-24), complicated avionics.
Plus, they are designed for heavy loads. Against insurgents a load of 5 Mk.82 on a F-5 at a range of 400km is sufficient as you will seldom encounter a larger target, most times a sortie means 2-3 bombs to do the job.
I said 100 Kowsar because its about 3 times the size of the Russian force in Syria to make up for the lower capability which brings higher availability. Higher availability is of more importance than load against insurgents.
As for ballistic computer: Russian Su-24 have one too but I'm talking about a SVP-24 like system. Something revolutionary not even 4th gen. Su-34 ballistic computer can compete with. This is the real game changer here and why Russian were successful with their small fleet. If the Kowsar has such a system as they hinted to, it would be the key to keep attrition low enough to be a cost effective weapon.
As for survivability: This fleet of 100 Kowsar would be fragile glass if attacked by US airpower. HOBS missile are the last defense and operating close to the own borders will provide it with advance information about incoming threats. But they main solution is: Drop the dumb bombs, push to afterburner and try to get back to your base at mach 1,5, it likely will be close because you are doing CAS and never fly more than ~400km away from your base. Honestly, the relative high speed fleeing capability is one of the main reasons why a F-5 airframe would make some sense in 2018, main points like easy and cheap operating costs aside (plus decent maneuverability).
I don't think they changed anything in the Kowsar that could make it any bigger. It is a 1:1 F-5 airframe. I also don't want to see an air refueling capability on the Kowsar. It is a cheap CAS fighter never operating in a hostile airspace far away. The overall system would become too expensive if you would want to get it tanker support, that's for more strategic aircraft only.