I'm fairly new to recording, and I've managed to get tracking down fine, but I can't play back all the tracks simultaneously without there being a ridiculous amount of latency. How am I supposed to mix, adjust levels, etc when I can't play back all the tracks? I am using large VSTs (amplitube and superior drummer mostly), and I think this is causing the problem. I need these VSTs though, so I need to find a way to make it work. I'm running all instruments (besides superior drummer) and vocals into a presonus fp10 into my laptop using Reaper as my DAW. Sorry if this has been asked before. Thanks in advance.
Get a better computer and/or learn to make decisions and bounce each take you want to keep to a new audio file.
What's the specs on your PC?

Assuming you're using ASIO4ALL, you'll need to reduce your buffer size. Too low, and you'll get all sorts of weird noise. Too high, and you'll get a ton of latency.

There's also a very useful bounce tool in most DAWs (I haven't used reaper in ages but it undoubtedly will have it) called FREEZE.

Say you've finished making your MIDI drum track for Superior, just hit the 'freeze' button and it will mix down the drums into a single stereo file on the same track, and unload Superior.
This means Superior is no longer using up any RAM and CPU time by triggering samples, it's just the same as any other audio track.
If you need to tweak it, you can just unfreeze the synth and carry on where you left off.

Do this for all the VST instruments you're not actively working on, and you shouldn't have to worry about low performance.
Also you can try increase your playback buffer. It will be in the preference. Set it up (as 1200 sample to 3000) when mixing this will somewhat improve performance. Just remember to pull it down when recording. (it increase latency for overdubbing) .

Or buy a new computer or bounce plug ins to audio