@GtBFilms Thanks for the info. I had a look at the ROM libraries I have for the emulator on my Mac and they don't even total 1GB, so that will give me plenty of room for other 'stuff'.
I've borrowed a keyboard from work so I have that and the memory card in my possession: the RPi was delivered today but whilst at work, so it's at our local depot.
Looking forward to getting my hands on it and getting started now: I have the Retropie installer downloaded and Retropie itself, my ROMS are all in situ and ready to go: so now it's just a case of build, install/setup and hopefully I'll be good to go!
I like the idea of having it connected to WiFi, I'm not going to install a tonne of ROMS, just my old faves and a few never-played titles, so being able to transfer one or two wirelessly now and again would be really handy. Plus it is 2016, so really WiFi setup should be a given!
Thanks for your help: no doubt I'll have more questions thrown up after installation, but fingers crossed it all goes ok!