Gameplay wise there is not much room what you can do bring Moldavia and Wallachia closer to their historical performance. In fact, the romanian principalities had to fight magyars and tatars quite frequently as well, not just the ottomans.
I would offer though to consider some events/missions for Bessarabia province. It was a strategic black sea shore and there were quite many powers involved in controlling it. It threatened the Genoa trade, which in turn motivated them to bribe crimean tatars to invade Moldavia. And it was also an important fort which Ottomans put a lot of effort to capture which the ultimately did take in 15th century and thus cut moldavia from sea.
I would offer though to consider some events/missions for Bessarabia province. It was a strategic black sea shore and there were quite many powers involved in controlling it. It threatened the Genoa trade, which in turn motivated them to bribe crimean tatars to invade Moldavia. And it was also an important fort which Ottomans put a lot of effort to capture which the ultimately did take in 15th century and thus cut moldavia from sea.