The only reason I can suggest for delaying a move to 2012, is that you have an existing domain architecture that won't cleanly upgrade. But since you have NO Active directory deploy yet, I take it that you're using the whole LAN in "workgroup" mode and without any domain at all, this is a trivially easy case to install Server 2012 on, and the new tools are the easiest tools yet, for creating a brand new ActiveDirectory Domain Controller and related infrastructure. If however, you mean you're still using Windows NT Server, pre-Active-Directory-domains, then I don't know if you're even going to get that all the way up to 2008 R2 in one go. You might want to update your question and specify what you mean by "having No AD" right now.
Get a book, either way you go, and learn about ActiveDirectory before you deploy it. I am running a mixed 2012/2008R2 domain server environment at our office, and I find that while I know the existing 2008R2 tools better than the 2012 tools, the 2012 tools are superior in every way, except for certain odd little tasks, and you can still access the old 2008R2 user interfaces if you want to, in 2012.
Both Windows Server 2008 R2 and 2012 are fantastic products. I see no reason not to deploy the latest version (Server 2012) in small LAN environments or for brand new ActiveDirectory deployments, and many technically advanced features in 2012, that are good reasons to prefer deploying 2012.
In large network environments with existing 2008 R2 infrastructure, obviously, there would be sensible reasons to deploy more 2008 R2 domain controllers, instead of moving only part of a huge 2008R2 network's servers up to 2012.
Best Answer
One DC should be able to handle the authentication load from that just fine. If you have all authentication traffic centralized at a single location, I'd start with just two and make both Global Catalogs (for redundancy) and only add more if you need it.