RetroPie Roms over 167,321 roms!
As you know. Don't download anything you don't all ready own. :)
You need to copy all the rom folders to a USB stick then plug it into the Raspberry PI (256gb drive)
Now follow the info on http://mardell.me/blog/how-to-load-roms-from-a-usb-drive-on-retropie/
You will need retropie all ready installed to use. https://retropie.org.uk/download/
Total Files: 167,321 File(s) 195,697,145 bytes
NOTE: Some folders are empty they need to be there for the config file to work.
Note: As for Mame Do Not UNZIP the files that will break the roms.
You are going to need a keyboard and mouse to play some of the games as well.
Network Install of roms:
To running it from a network share works lots faster and shit ton more space.
edit /etc/fstab add this line (well for your setup) USE IP for server (static if you can) user/pass is whatever you make the account for. It needs read / write
Make a new line and add this and change it for your setup.
//192.168.1.169/Roms/roms /home/pi/RetroPie/roms cifs username=osmc,password=osmc,nounix,noserverino,defaults,user,exec,auto 0 0
//192.168.1.169/Roms/roms <-- change to your settings
/home/pi/RetroPie/roms LEAVE ALONE!