How big of an SSD is needed to put something like Ubuntu on? Ubuntu comes with most things added on already so there won't be much else on there. I've read to use around 120, or whatever the standard one around that size is, for windows, but Linux is wayyyy smaller so it shouldn't need as much. What would you recommend? In the end I'll have an SSD as a boot drive and 4 HDDs running RAID 10, I may even eventually get a 2nd SSD and run raid 0 for a boot drive. Also, some help with how to set this up properly would be nice as well.

I've been using a (cheapie) 64G SSD for 11.10, 12.04 and 12.10, with unity plus many more programs for over a year and a half now. With absolutely no problems.

I have run many modern linux distro's on an 8G usb so it ought to do fine on anything now sold almost in a ssd.

Each brand and version of ssd may have some issues to look at. Most of the common ssd's have tips to help you. Decide on one and start searching of just load it up and see how well it works. There are many many people to start off by updating the firmware on the drive. Not sure if that would be my first choice but too many people report that it fixes issues.