What do i need to build in order to train janisary heavy infantary?

[caravel]

Agreed. If the Military Academy was dependent on just the fortification, it might be more worthwhile. It would be even better if one only needed a Citadel or maybe even a Castle to build it--except that would give the Turks a bit too much of an edge, as they could then train Janissary troops just about anywhere and spam them like nobody's business.

Yes, with the mod I'm working on the Military Academy will only depend on the Fortress, and not the Fortress and Grand Mosque or Fortress and University as it does in vanilla (so multiples will be easily possible). Janissaries will not gain valour bonuses from any provinces (Bulgaria and Georgia bonuses removed), and will also be restricted to the Late period only and only trainable in their homeland provinces (an area roughly equivalent to the Asia Minor portion of the Ottoman Empire comprising of Greece, Bulgaria, Constantinople, Nicaea, Trebizond, Anatolia, Rum, Lesser Armenia, Armenia and Georgia).

Sounds restrictive but if we were doing it historically they'd be only trainable in Constantinople during the Late period, and the Grand Mosque and Military Academy would both still be required.