It's almost impossible to find an OEM machine without Windows 8 from a website (and impossible if buying from a brick-and-mortar store), so I would strongly recommend a machine with more than 4GB of RAM. 6GB is the absolute minimum I would go with, and more if at all possible.
4 GIG of RAM strikes me as low for your needs and even for computers in general.
Aren't most people still running 32-bit operating systems though
Only a 64bit OS is capable of recognizing & utilizing over 4GB of RAM. I've been on 64bit WinXP & Win7 for several years and running 8GB of RAM.
The next machine I build from scratch will probably have 16GB, since the motherboards & BIOS are now capable of recognizing that range (or higher).
, how comfortable would you be building your own machine? I did that, and while I spent a ton of cash, it was far superior to anything in the same price range that was pre-built.
I was able to pick & choose what brand parts I wanted. You could still do it on a budget, maybe reuse your current case and other components that are still good.
Then you can buy a full license of Win7 and set it up exactly how you want.