I had (and still have) these same questions. I've read TONS of material on what to buy and what not to buy and here's the conclusion I came to: only buy enough to record your guitar into Reaper, and stop there for a long time. (I tried Cubase LE and Ableton Lite and compared to Reaper I think they suck. But whatever, they all can probably do the same stuff.) My reasoning is that I'm simply not skilled enough to hear the difference between good PC speakers and near-field monitors, or pro-grade A/D converters and entry level, or an acoustically treated room and my spare "music room." I think spending more than a couple hundred bucks just to set yourself up is going to be wasting money, but please defer to someone with more experience. We all want to be stars like Pebber & Ursin (et. al.), but if we ever do get sponsorships then we can upgrade our stuff later, right?
I own the Line 6 GX audio interface which comes with Pod Farm 2.5 (guitar & bass). I'm not stating this to shill for Line 6, and in retrospect I wish I got one level higher to have an instrument input and an XLR/balanced input. Nearly all of the major brands make an entry level audio interface and most come with software. I picked Line 6 purely because the POD Farm marketing sold me. Is it good? If you don't have a tube amp with a line out, yes, it's very good. (Notice Pebber uses a line 6 solid state amp in most of his videos. Same programming as in Pod Farm.) In truth, I am lucky enough to have a tube amp and an attenuator with a line out. So now I only use Pod Farm for bass guitar. I still use the GX though as my audio interface and aside from the single input problem have never had any problems at all.
I own a decent set of powered PC speakers (Klipsch promedia 2.1). Are they good? Yes. Do they put out an unbiased signal with a flat response? Heck no, the bass is boosted and the waterfall graph sucks. Can I tell? No. Have the 5 people that have listened to my music ever complained the bass was too high/low, or that instrument X wasn't cutting through? HAHAHAHAHHA. No chance. Would i buy the speakers again if I was starting from scratch with what I know now? No, I'd spend $50 or so more and buy a pair of 5" near-fields. I very likely would not be able to hear the difference AT ALL, but if I stay as motivated as I am now for another 5 years I'm betting at some point I will.
I hope this helps you, but I'm afraid this might be a case of the blind leading the blind.