Curtains do virtually nothing. You will want foam. Any kind of foam will do; if you're okay with giving your information to the Chinese botnet you can get it off Alibaba for less than a dollar a square foot. Or you can repurpose old packaging foam and manually cut it into the classic crosshatch/pyramid shapes if you're strapped for cash, but acoustic foam has come down to a price where pretty much anyone can afford it these days.
I used the wrong terms when I said "preamp" and "mixer". The Scarlett Solo would be fine for the purpose you have in mind. Always worth remembering, however, is that you need things to be as close to perfect as possible on the hardware end, because the more digital tricks you apply to the recording to more obviously fake it starts sounding. If you use or plan to use Cool Edit I have an excellent speech preset I use for spoken word dynamics processing, but again, making sure that your volume and levels are good before
recording is key.