'09 mac mini hardware upgrade advice
The 2009 and earlier model Mac Mini all lack the black small round access port, so are much easier to get at the hard drive than the newer thin "unibody" Mac Mini computers.

I really like RamJet for checking which machines can run more ram than Apple places in their "what we support at the time the hardware is released" manuals. They only sell to Macs, so really have to work hard to mix up your models or get the wrong ram. Where you buy is certainly up for debate, but the RamJet tools are the nicest I've seen.

As to your hard drive exchange - the SSD will replace the HDD easily. Putting a second drive will be less easy as I'm not aware of a mounting kit for the optical drive attachment in that class of Mac Mini. Do your homework well or get a good return policy if you find out your drive doesn't work when connected to the optical drive SATA connection.