I have played RTW and M2TW and I am more used to them. But this game is awesome.
and the enemy keeps on wanting to attack my flank with his entire army which is annoying.
Welcome to the world of Shogun and samurai warfare If you're used to playing against the RTW-style AI, you will get a rude awakening here

I have trouble using musket units.
Look around for some of the topics here that discuss using teppo in detail. Also, take a look at some of the campaign AAR's. Many are full of tactics using guns............