I would rather that Indonesia NOT induct the J-10 at the moment, as your air force is already committed to 2 fighter aircraft types (F-16s and Su-30s). The J-10's WS10A* engine is not a 'proven' product (as early versions of the J-10 were using the Russian AL-31FN engine), so Indonesia cannot know how much parts to stock for the WS10A engine. Don't subsidize China's WS10A engine development by being their first sales guinea pig (let someone else be the first few foreign operators of the J-10). Why make your air force's life so hard in maintenance terms (you already have hard to maintain Su-30s)... and you have so few of each aircraft type any way.
OPSSG, I think you just hit the main issue, standarizations of aircraft types. The Air Force love their F 16, and deep down if they can choose, they want to replaces ASAP those F 5 and Hawk 200 (useless fighters if I might say, bought only due to Soeharto's cronies business) with F 16.
Before I put J 10 only for possibilities (distant but still there) of the comebacks of the previous Soekarnos daughter as president. After all her political block is the one whose fanning the anti american sentiment in here.
The current defence minister and the air force chief in several interviews already hinted they want more F 16. How to get it is the problem. Definetely (from sources in the air forces) we want 60 to 72 F 16 and if that can be achieved only 12 to 24 that will be brand new Block 52. The rest will be upgrading (MLU) of existing Block 15 and second hand Block 25.
Just like you say, that's the budget problem will show.
Realistically though If we upgrading F 16, it will come from US Inventory. Don't think at this moment there will be much extra non US F 16 left. We already missed that since Jordan, Chille, and other NAto's eastern members scoop them.
Please do not propose to operate 12 fighter squadrons -- it is the most inefficient way to run squadrons (as each squadron will need tooling, maintenance manuals, parts and so on). I would rather Indonesia operate fewer but bigger squadrons of 18-24 planes each and rotate them via forward deployments of detachments to different Indonesian locations (you'll have less crashes that way), as and when, Indonesia feels the need to beef up security in a particular sector.
I put the number 8 as the air force 5 years plan still call for 11 sq's in which 8 fighters and 1 COIN and 2 specialize ground attack. Don't now why they still need COIN since with the MI 35 in the army, no need for this type. Also with nature of multiroles of current fighters, specialize ground attacks is redundant.
But it's the nature in planning here, that you ask for more and settle for less. Thus I belive the airforce (from other interview) will settle for 8 sq.
Again if they want standardize with SU 30 and F 16, the most realistical and optimist number will be 72 + 24. More of that beyond affordability unless suddenly we can have more than USD 10 bio defece budget annualy for the next five years (Tripple from what now

)
The questions is 12 fighters per sq is it optimal ? The airforce wants to have 18 per sq, but if we can only have below 100, than 8 simply out of questions. 8 because the airforce want to have 8 fighter main bases.
Rotating them off course is what they're doing now (with only 5 sq of fighters), and even with 8 sq they will also still rotating them to secondary bases.
Thus came argument that 12 per sq still can achieve optimal maintanance capabilities, that as long as we can have overall quantity numbers that spreading them in several sq still maintanable.
But personally I agree that's this means still higher maintanance costs. But sadlly theres still bonehead lawmakers in here more attracted to hollow national pride and prestige on having more sq eventhough it's means having less aircraft per sq.
I'm just hoping by the time the money comes for getting those aircraft, it's also means getting the missiles and the other armaments. The situations with the first flankers purchase hopefully not to be repeated again..