Your first focus should be on acquiring the advanced med hub and the defibrillator. Immediately following that, the two general player sprint upgrades.

As for the rest, approach it as all other things you are new to. If you're at you're playing your first notes on the piano, will you approach a five hour opera? No, you'll start with simple songs and move on forward when you've got that simple thing down pat. You'll start with well-established songs, with easy melodies, and then you will gather experience, move on, and start focusing on things you didn't even realize were beautiful before. You'll be able to decide, after playing easy things, what is hard and what is easy: you'll be able to decide what is pretty and ugly for yourself.

Same goes here: take the middle road, fit with the crowd. Once you understand the strengths and weaknesses of the common items, approach the more exotic, more imbalanced things.

To that effect, a sure road is a medic. You help out your squad but you don't exactly kill a lot of people. This is the safe, balanced road.
With regard to weapons, the safe balanced weapon is the Voss. It doesn't pack as much of a punch as the Krylov, but it has a larger clip. It isn't as good for long-range engagements as the Baur, but it is more accurate than the Baur.

As a newbie, use the Voss. Understand its strengths, gain experience. Once you realize where you stand, expand into exotic territory: use the Krylov and the Baur. Which one is better?
You'll hear about a billion things on that subject, and mentions of Hitler will inevitably come. Don't ask what is better: ask what is the safe road for a newbie to take.
Once you have a ground of experience, you'll be able to decide what is better for yourself ... and promptly change your opinion every two weeks.