Haven't played for a while, but I'll stick my 2 cents in.
Armies: Warmaster armies are generally quite balanced, although i tend to think cavalry is a bit good for what you pay for it, but generally in Warmaster I think you'll get a good game out of anything. In the early stages of playing people tend to find high
LD armies and Cavalry armies over powered perhaps, but in part thats simply a matter
fo learning the system. Perhaps a more specific opinion might be formed by looking over the comments on V2.2 lists in the Spec Games forum, at least as to which units really don't work (steam tanks for example, ain't so great). I wouldn't do lizards as a first army, unless you have a real attachment to them. Their special command rules means you have less control over tham as an army (characterful, but perhaps not so much fun if this is your only warmaster force)
Brigading is just in battle method of ensuring all stands in a formation recive the same order. Warmaster's basic command system requries you to nominate a unit, roll the commanders
ld and if you pass, the unit can move. If the command roll fails, the unit cannot move and the commander cannon issue any more orders for that turn and neither can that unit be issued any more orders that turn. If you are trying to preserve a battle line of 4 units (and generally you will be as a staggered formation is more vulnerable), this would present a problem if you were advancing each unit one at a time - even on Ld10 you'd fail a check in mid line at some point and your battle line would be all over the place! Brigading allows you to issue for units that are touching each other a command together, so they pass or fail as one.
Brigades are decided ad hoc, you don't really need to worry about them at the collecting stage. You wouldn't brigade cavalry with infantry as they move quite differently, but then i wouldn't have thought you want you cavalry in the centre of your infantry line anyway. Brigades can be formed at any time, so you could brigade as much as possible in turn one, to keep your shape on approach, before forming a battle line in turn 2. Its very situational though.
I really like the ruleset, although i think the warmaster ancients limit of 2 combat rounds is a necessary house rule (whether this is in the living rulebook now, i don't know)