Okay, regarding your data:
You have a few options here- you could do an upgrade install, which will preserve everything or you could install to a separate drive or partition. I recommend the latter option, however because...
This is not ideal for a main PC with important data. This is beta software, and while it is a fully functional OS, it will have some problems along the way and at the end of the beta period you'll have to install something else anyway (and if this is like previous betas, that may mean doing a clean install of Windows). If you want to try using this as your main OS then do yourself a favor and dual boot. That way your old OS and everything that goes along with it will be safe and you can go back at any time if there are problems.
Bugs will happen. Most will probably be minor, but I still would not go all in. If your computer is seizing up or crashing and you need to get work done, but don't have another OS to boot into you are going to regret it.
All that said, I don't see any harm in trying this out. Just go the dual-booting route.