Not just being contrary, but I'd recommend against using terrain and weather rules early on. You're right to start with small armies, but I'd suggest you use them on tables with no terrain.
DaveMather is right that terrain is an integral part of the game. Consequently, not using terrain will make certain troops a lot less useful. But the key with learning this way is to take the rules piece by piece, rather than concentrating on the best ways to use troops. This means fewer rules to learn in one go.
Early on, I'd recommend concentrating on things like the combat system and movement system. Then, once you're reasonably familiar with them, introduce the terrain rules. Then weather and time of day.
The best comparison I can think of is learning to drive a car. Even if you plan to drive a manual, I'd recommend learning to drive an automatic first, so that you can concentrate on the business of interacting with the other traffic. Then, once you're comfortable with that and have your licence, learn how to drive a manual.
Having said that, though, the best way to learn DBMM (as with so many other games) is to watch other people playing it, and maybe take a command. I realise, though, that this isn't always possible.