I'd start out using what you have. As a beginner/cat 5, your wheels won't really be holding you back. I have a bunch of riding buddies that always use their equipment (or lack of it) as an excuse not to race. The fact remains that in every race I've been in, there has been at least one crash and you won't want to be worrying about a $1000+ wheelset. Any wheelset in the 1600g range should be adequate.
Also, you really don't need carbon rims if you are traveling in a pack.
To get proper carbon race wheels, you'll want tubulars, and that is an additional expense- plus you won't want to be training on them as well (fixing a flat tubbie?!). If, as you say, you can only afford ONE set of wheels, you'll likely be stretching your budget. For the same price as any of the options you mention, you could buy two sets of aluminum-rimmed wheels.