Nick, I record guitar(s) at home the same way you are planning, and yes, the first thing you will need is an interface of some type. I use a Presonus 2 channel USB interface, a lot of people here use the Saphire products, all work very well. In my setup, I have a mute switch on my Fender Bassbreaker tube amp that lets me mute the speaker, (I live in a condo and my neighbors don't appreciate my guitar wizardy. :) ) but I still get output on my XLR line out that I connect directly to the interface. However, if I wanted to, I could just connect the guitar directly to the interface, then use amp/cabinet sims on that track to get the tone I want. As far as recording levels, that's all done through the interface. The rule of thumb around here seems to be that you set the input level on the interface to where the signal is showing around -18 db on the meter. But in my setup, going through the amp and pedal board, getting that level on the interface introduces a lot of noise so I crank the interface input level down below that noise level, then use tools in Reaper to boost that as needed in the mix. I'm just a home/hobbyist so that works for me.