You're going to be very limited in that space as far as professionally mixing and mastering audio.
When it comes to mixing/mastering the most important aspect is your room.
You need to get it acoustically treated properly. (No, this does not mean go buy a box of auralex and slap it in random spots of your room).
Proper acoustic treatment can be done with Roxul (A very dense insulation that can be purchased at Home Depot. It performs way better than Auralex - which does close to nothing- and is cheaper than Auralex as well). It'll require a bit of work from you to set it up but the end product is worth it. The panels are VERY easy to make. You'll need to buy some wood, a few screws, your choice of cloth to cover the panels, wood staples, and you should already have a hammer and screw driver. If you don't have them already you'll need a staple gun which can run $20 and a circular saw $75 or a hand saw for $20. I could make a whole thread with step by step instructions on how to make cheap, incredibly effective acoustic panels for any situation. Let me know if this is something you're interested in and I'll walk you through it.
Roxul Safe 'n' Sound 3 in. x 15-1/4 in. x 47 in. Soundproofing Stone Wool Insulation (1-Batt)-RXSS31525 - The Home Depot
If you can't (or refuse to) acoustically treat your room I would tell you to adjust your expectation as far as mixing and mastering.
Without a treated room you will not hear how the music actually sounds, instead, you will hear how the reflection of your music sounds. The result will be that your music will sound completely different from one source to the next and ultimately your mixes will suffer. You'll be making mixing decisions based on the reverb of your room and not what the actual characteristics of the sound.
That aside, the next thing to tackle would be the vocal quality.
Every studio needs one of these.
SE Electronics RF-X Reflexion Filter X Vocal Booth
You'll see in my studio pics that even though I have an acoustically treated booth, I still use one of these.
In a room with no treatment at all, it isn't perfect, but it definitely helps isolate the sound more.
The Scarlett interface is a decent starter interface.
The mbox 3 is a good one as well if you have a little more to spend.
On the high end you have the UA Apollo which is the next upgrade for the studio I'm looking at as well as a new iMac.