TLDR: shouldn't be too difficult, depending on your needs.
Much depends on what you want to record.
It's a small room, which can be problematic for certain applications. I am happy you said "sound good" instead of "sound proof." You aren't going to be able to do much in a small second-story room to make it quieter.
If you're not recording drums and can record bass direct (and maybe even guitar ITB) you aren't going to have any real issues recording; you can skip the heavy bass-trapping and maybe even just use a little treatment to tame the HF early reflections. Maybe pick up a large diaphragm dynamic mic for vocals like an SM7 or an RE-20. They sound great and will help negate most of the reflection issues you're going to run into, at least in a vocal application.
Assuming no live drums and loud amps, recording-wise you should be fine. Creating an accurate listening environment a small square room will be more of a challenge. Try and set up so that both sides of your listening position are symmetrical with identical treatment. Treat the back wall. The room isn't big enough for diffusers. If the ony thing you're recording live in the room are vocals, you can probably even get away with foam rather than rockwool or OC703. You'll need to learn how the room affects how you're hearing the mix, and that will take time and a lot of listening in different environments and different speakers, even headphones. The goal isn't for the mix to sound "good" at your mixing position. The goal is for the mix to sound accurate. That's a challenge even on a big budget and with a large room. You just have to take the time to know if the bass is boomy in your room because of the room or because of your mix.
