Before I could answer your OS question, I'd need to know your system specs.
As far as the SSD goes, it depends. Right now, an SSD is best used for a OS drive and for applications. They're relatively small, and while reliable, they do have finite lifespans. A hard drive will usually give you a warning it's about to die giving you time to backup your data. An SSD won't. Hence why it's not a good idea to use it for long term storage.
Further, with MAME, you'll notice no difference if you store your roms on the SSD. The majority of games are so small that the throughput of an SSD is wasted on them, SSD's throughput shows when you're loading many files or a large file, files that are a couple of hundred kilobytes won't benefit significantly.
That said, I love my SSD and when I build my next system I'll use one again for my OS drive. Loading windows, or games, is incredibly fast. In fact, the biggest drawback I can think of is that things load so fast that all of those tips they put in games on loading screens are gone before I can even read them since load times are a couple seconds at worst generally.