hey bud!
nothing ever comes simply and learning about the best army (imo) in fantasy is no different! you have already done the best part and found a very active forum with plenty of voices (some that are abit louder than others

) my first advice would be too look at the threads regarding state troops and detatchments, these are the very core (literally) of our army. the size,formation and equipment have all been covered in a few very decent threads.
my advice for infantry is more is better units of 20 just dont work.
next you might want to read some of the grand strategy threads or the tactics thread (there is a good one in the first 2 pages of this forum). The gist of the thread outlines that you never put something in your army without a specific plan for said unit. so you might have a 'hammer' unit for your anvil of state troops, perhaps some artillery to soften up the enemy before he strikes or even some BS shooting troops to help protect a flank
my advice is take artillery but dont go crazy, if your gun heavy and your opponent has lots of scouts/ambush/flying whatever artillery hunters, they simply wont be as effective. (my example here would be i take 1 mortar @ 500-750, 1 m 1 c @ 1000, etc etc)
honestly just read over this board and search for any units you have questions for, i can guarentee most of the units in the book have multiple threads devoted to their use and benefits.
finally good luck! empire arent the cakewalk some armies are, indeed there are many pitfalls in collecting a jack of all trades type army but that is what makes it so much fun
