Well, a few things I would say:

First of all, for starting factions. Spain is my recommendation. They have lots of titles, lots of rich provinces, access to elite late troops as well as having early stalwarts to boot. Additionally, some very powerful historical generals, like Pizzarro and Cortez who emerge early. Plus, the tactical situation of Iberia gives an easy to defend situation, unlike France who can get ganged up on.

Battles are a very different monster for most factions in this game. Early on, the best units will be "mercenary" units who require an inn to be trained. These include a couple variants of pikes, a musket unit, and a zweihander unit. The pike and zweihander units are incredibly powerful in melee, and will decimate almost all non-merc units in melee. The musket mercs are fairly substandard in melee, particularly in comparison to the pikes and zweihanders, but are your best bet for trying to wear down the giant pike units who, though very powerful and pretty well armoured, are quite slow.

Early cavalry include light lancer units who basically exist to run down archers(yes, there are some still left around to train in the "early" period of the game) and muskets. They hold no water in melee and are generally quite weak. After a bit though, you'll be able to start caracole units, who are essentially mounted pistol wielding troops. These guys are great for harassing the pikes and zweihanders for ages and ages, particularly in western europe and the eastern steppes.

As the game progresses, you'll get to a point where you can start training more "native" pikes who are comparable to to the mercs, at least as Spain. Spain has various Tercio units who are considerably cheaper(not that the Spanish need to be thrifty ). Other factions tend to be later coming in such native powerhouses. Anyways, after a bit you'll get to the point where battles are basically, well, pike and musket battles (). Battles can turn into giant, field long skirmishes of each army trying to out-position the other while trying to concentrate fire onto individual units to cause routing. Lots of fun.

Also, if you're in the mood for a bit of exploitation, regimental cannons are monstrously powerful units. Mobile cannons who fire in barrages of four shots. Quite accurate, and given they only have four men each, they pile up valor like crazy. I had a battle as the Ottoman Turks(defensive one, I should point out) where I literally had zero casualties against an army of roughly 1300, because I parked on a very steep hill and had 6 units of regimentals, in addition to a lot of muskets and horse archers. Enemy never got within firing range.



Factions to watch out for(ie, the powerhouses): Spain, Ottomans, Russians, and potentially the French. Russia will often stampede Eastern Europe with giant armies of very poor and badly trained troops and will often simply smother other factions with a giant zerg rush. Spain and France are both extremely rich and have lineups stuffed with powerful troops from top to bottom. Ottomans start with a lot of territory and have some of the game's best troops in the mid-game.



Hope that helps.