All items are unlockable in-game (other than new armies) and most of them offer only cosmetic or marginal improvements which only give a slight bonus to only a few units. You will not be at a severe disadvantage in any way. Wehrmacht is very cool to play though and probably one of my favourites in general. I personally played Soviets online and did fine despite the fact that there is a general Axis preference. You're not going to get owned online, since both of these are very competent on their own. You can always buy additionally the other armies and I would personally recommend it since it really starts spicing up when you see what kind of combinations of armies you can play. If you get the base game you get the Soviet campaign which is enjoyable (and do ignore the criticism around it, it's perfectly enjoyable if you're willing to accept that war is crap in general), a very nice set of Theater of War solo and coop missions and two factions which are the Wehrmacht and Soviets and a whole bunch of maps. I've been playing it a lot and I really recommend it regardless and on top of the fact that I was a huge fan of the original.

COH2 is much much better than it was at launch. Just to give a full reply to the question.

Company of heroes 2 which dlc