Although I mostly play keyboard by ear, I had a book called, "The Chord Wheel," by Jim Fleser. It is a great reference book and it will help a lot with chord theory. I've been formally trained on the sousaphone/tuba and I've been involved with band from the 6th grade up through college. This book even helps with transposing keys if you even decide to write orchestral scores.
I feel you on this one here. Before I upgraded my PC, I invested in an audio interface (Roland UA-4FX ~$90) around the end of 2010. I had it running on an old Gateway PC that I purchased back in '02 while I was still in college. It took a lot of the processing load off of the system memory and I used the interface's ASIO driver which cleared up a lot of under-runs and latency issues. However, when your're get plug-in happy on the effects side, the interface can only do so much and if you don't have the RAM to spare you're still gonna have issues. Right now when I'm on my laptop I'm good w/ 4GB of RAM, but on my desktop I have 8GB and I'm looking to upgrade to 16GB.
I'm thinking of investing in a midi keyboard, but for now I'm using an Alesis QS6 Synthesizer which works well for me, plus with the interface I can play some of the stock keyboard sounds into my work.