Sweet! On the off chance you haven't found it yet, I'm going to link this super helpful vlog.
All just a bunch of tips and tricks for Reaper. This in particular is great - basically helps you download a buttload of tasty JS plugins all at once.
As far as mastering is concerned, I typically start out with this FX chain and remove plugins as I see fit (I almost never use the EQ they include in this chain). I don't really care for the way they set up the multi-band compressor (the EQ feels wrong for a lot of songs), so I usually fiddle around with the settings until it sounds better. If you're just looking for "make this louder", all you really need is the limiter, though I would put on some light compression on the master track before you limit it.
PS, let me know if you ever want me to check out your mixes or give some help with Reaper - I'm far from a professional, but I am a second set of ears!