@sam Setting up RetroPie on a real RPi is easy if you follow the instructions (which you've presumably already looked at when you installed on Ubuntu), and the forums are full of extremely useful information (sometimes better than the documentation :P)
Have realistic expectations tho; while the vast majority of platforms are emulated pretty much flawlessly and PS1 emulation is mostly very good if you overclock your Pi a bit, N64 and Dreamcast are really at the very limit of what can be achieved on the Pi3.
If you're cool with that, and maybe asking a question or two here if/when you get stuck, then in my opinion there's no reason not to get an RPi3.