I've been thinking about doing the same thing! I started really exploring the idea this weekend. I haven't uploaded anything, but have been looking into microphones, software, etc. I currently only have a headset with a detachable boom mic; it's not very good audio quality.
1. Dunno either (for myself). I've watched a few TS3 Lets Plays and those players are pretty much talking the entire time. I don't know if that's good or bad. I think you'll eventually learn how to comment while playing and get better at it. I've also been recording my own TS3 videos and listening to myself commenting on my own gameplay. I'm not doing too well; not speaking what I'm thinking enough and often not speaking clearly enough. I've decided I should really practice recording and listening to my videos before I even think about uploading anything. I need to get more comfortable with commenting, and deciding what to show and what to later cut out, and develop my own style.
2. Don't hesitate to record yourself anyways (if you haven't already) and watch your recording to see how it goes. I was surprised that my voice sounded much better than I feared, although it's still quite tinny due to the microphone I'm using. I've seen the Blue Snowball iCE recommended for beginning YouTube gaming videos and that's about $50 or $60 on Amazon. If I decide to take the plunge I might try to pick one up on Black Friday. That's a bit away, but after watching several "how-to-YouTube" videos, doing them well is a bit of a learning curve.
3. Recording: OBS, or Open Broadcasting Software, is free. It's mainly used for broadcasting to Twitch, but can also be used to simply record to a file. It's fairly easy to adjust microphone volume vs. game volume and there are plenty of tutorials on how to use OBS. I've been using it myself to play around with. I think it's decent enough to start off with, and for voice practice you don't need to worry about final video quality.
Other popular programs (from what I've read) are FRAPS, Dtoxy, Bandicam, etc. They aren't free, but they have a trial version with some limitations. I happen to have purchased FRAP a while ago, it was $37 or so IIRC. FRAPs allows you to record game audio and mic, but you have to set the sound levels in Windows - which meant a lot of trial and error for me because the mic volume was much too low. FRAP is quite popular so there are tutorials on how to do this (but many are out of date). FRAP and Dxtoxy produce absolutely massive file sizes with little compression (to have as little impact on game performance as possible). You'll have to compress them before uploading to YouTube, and unless you have tons of hard drive storage I'd guess you'd want to keep the compressed video and delete the FRAP capture as soon as you are done with it.
Another option is Nvidia ShadowPlay. It's beta and only works on higher end Nvidia cards - the 660 might be one of them, you'd have to check. I haven't tried ShadowPlay yet, but I've read that it captures game and mic audio, and it's free. I don't know what kind of file sizes it produces. Look for some YouTube videos reviewing ShadowPlay (or any game recording software) to see it in action and hear some opinions.
You can also record gameplay with one program, and then record the mic using Audacity (free) and sync them later with your video editing software (again, so I've read). But that's 3 programs running on your PC (the game, the game capture program, and Audacity) which may impact game performance. The advantage seems to be that you can later alter the volume of the mic/game in your editing software if necessary, when you combine them into one file.
Video Editing: I haven't gotten to editing or encoding videos yet. I was looking for free video editing programs myself recently (yesterday, I think) and didn't find much. I downloaded a few to try out but I don't know if any are featured enough. I think Microsoft Movie Maker is popular, and it's free with MS Live Essentials, but I've read it very simple too. I will probably try it out at some point. I suspect that if I seriously got into making Lets Plays, I'll end up buying video editing software.
Making YouTube Lets Plays seems much more complicated and involved than I thought, lol. I even stumbled across a video on how to design a good thumbnail for your video.
The only thing I've actually done, is recording my own gameplay with commentary and listening to myself (with TS3 and another game). That itself has been a real learning experience. I think I'm going to have to practice a bit to find my own style, then learn how to edit the videos so they look nice, then maybe (if I get that far) think about investing in a nice microphone, video editing software, and start making stuff to actually upload.
Didn't mean to write a book here, lol, but you just happened to ask when I just started to look into it myself. Good luck! :D
Oh, lastly, I think your computer is probably good enough. You'll have to try different things and see how they work out.
