ancker

I currently ride a 2008 Trek 1.2 (Triple).

I've been wanting to upgrade to a Trek 2.3 and probably still will later this year.
My main reason for wanting to upgrade is to switch to a double, wanting newer components, and have a slightly lighter bike.

My question is that if I were to procure a couple year old 105 or Tiagra group to hold me over until the new bike, what sort of things do I need to be careful of? Can I just replace everything and it work fine? Do I need to make sure the crank is compatible with my BB?

Thanks

Propofol

If you're going to switch out the crank you might as well swap out the bottom bracket as well, non-ceramic ones tend to be fairly cheap.

You probably have a 68mm English threaded bottom bracket, but check to make sure.

ancker

And while you're at it, where are a few good places to find a used group?
I've been browsing ebay but mostly finding new old stock for several hundred.