The common breakdown of recording from most to least important is Source (instrument, performance, room) and Chain (mic, preamp, effects, convertor). Monitoring should also be thrown in there towards the top, cause, as pointed out above, if you can hear it you can't correct the problems.
You have a good mic (esp. for rap or radio announcement work). If I was in your shoes I'd look to buy 2 things first. A good monitoring system would be at the top of my list so you can hear to record and hear to mix (that is a 2for1 deal). Next, simple room treatment. Unless your room is completely square or has other problems, it isn't too difficult to make it acceptable. A bed or sofa acts as a good abosorber, book cases (w/ books) does the same as well as adding some diffision. All you might need is a quilt to hang behind you when you sing to keep the back wall reflections for going directly to your mic. $25. I have one I can put up over a cable behind my singer's spot. You can spend more - a lot more - but there are lots of places to look for cheap, easy to make alternatives.
So, with your budget I would think a couple of hundred $ in room treatment would be all you need. That also does double duty - recording and monitoring. Monitoring ... I'd get the Yamaha MPS 7. $800, good bass extention and pretty flat. And if you get bored of doing music, they make a long lasting pair of listening speakers.
Lastly, a nice, high-gain preamp. The Focusrite ISA One is a good choice. Enough gain so you could use a dixie cup on a string to record and kinda middle of the road as far as sound. Neither too clean or too dark, but a Goldilock means. It should work well with Rap
or just about any style. The Warm preamp is another lower cost contender. More of a vintage vibe and really puts through a lot of bass. Either of those are $4-500, are well built and high-end enough you won't want to sell them when you hit it big. Professional grade equipment. Either of those (or the gap, grace, daking etc.) will allow you to use certain techniques that are hard if not impossilbe for built-in preamps to replicate. If you are a screamer, those techniques might be moot.
That gets you somewheres around $1500, so you have a little left over to start saving for your next purchase or get more room treatment.
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