Each aircraft type would have one training squadron correct?
So far TNI-AU does not have dedicated conversion unit sq for each type. Their practice always include the double seaters as conversion unit also as part of operating sq. So the F-16B/D always mixed with F-16A/C operational units or Hawk 100 also mixed with Hawk 200. Thus the double seaters basically having dual function for operational and conversions.
There's some French sources that put 42 Rafale order will consist of 30 single seater and 12 double seaters. Thus why there's possibility there will be 2 Operational Sq and 1 Conversion sq, however so far it's not TNI-AU practices.
This is why it would be better to just have 2 types of fighters as you would then gain 2 operational Squadrons
Yes, the ideal make up is Heavy and Medium-Light Fighters. That's why in this thread I already put the ideal Fighters configuration should be F-15ID and F-16V or Rafale with FA-50. Again Indonesia defense procurement is not only based on users (TNI) assessment, but also Political consideration. That ORBAT I've put in my previous post is a potential based on Political procurement choices. For Indonesia that's the most likely to happen.
TNI-AU from SBY era already put Heavy and Medium-Light combo in their plan. They always want F-15E for heavy fighters, however since US only give green light before for F-16, then Su-30 is the second choice.
During SBY administration, the plan is to build Su-30 with F-16 mixed for 2020+, with F-16 will gradually replace Hawk 200. Those F-16 will be then gradually replace also by KFX by end of 2020's decade onwards. That's one of reasons why they are looking for second hand refurbished F-16, as they are in the end will be interim ones until KFX come.
This administration seems have different idea. With Russia out of the procurement mixed, then they replace them with Frenchie. The question on KFX/KF-21 then become bit redundant with Rafale coming into the mix.
Can it be two types mixed in the end ? It's still can. It could be F-15ID with Rafale mixed or Rafale with KF-21 mixed (F-16 that I put in ORBAT, I suspect will be gradually on retirement path by 2030+ anyway). However Politics can also push for 3 types mixed of F-15ID, Rafale, and KF-21.
F-15ID is most likely will stay in plan, now US already give green lights, TNI-AU will insist on that if as Flankers replacement (I suspect that's why those Flankers only have minimal upgrade so far).
I do expect some opposition from US law makers that doesn't like Indonesia (and there're some of them in Capitol Hill). However since Trump already approved for F-15 in principle during his last days in office, and now Biden also give approval, I do sense bipartisan support can be lobby. If that happens, Indonesia will have no choice but to take the offer. Sometimes people forgot that Indonesia also have considerable trade surplus with US.
That's why if ROK still able to get through their Political Lobby in Jakarta, then three types can come to future TNI-AU fighters inventory. That's not much different with present mix of Flankers, F-16 and Hawk 200.
For me personally I do hope for F-15ID replacing Flankers as Heavy Fighters, Rafale replacing F-16 as MRCA and FA-50 (instead KF-21) replacing Hawk 200 as LCA. That's provide more balance fleet.