This is a good source of information concerning mixing ...
Mixing Secrets For The Small Studio - Additional Resources ...
Personally, I'm not so concerned with the room acoustic aspect, as it's very difficult to get decent results, especially for cloth ears such as mine. Instead, I bank on 'comparative' acoustics, whereby I listen to stuff I like in the room I have (or with my headset...), and compare my mixes to that. Any major flaws will be common to both sessions, so should cancel out, hopefully. Not perfect, but I'm not disposed to set up a 'pro' studio with my budget and modest needs.
On the site linked above there are scores of stem tracks to have a go at, and test one's skills and inspiration, all for free. Recommended to get a feel for what works and what works less well. I wouldn't use Audacity for long for mixing, although it's very good, and I use it a lot for other stuff. A full-fat DAW is what is required (I use Reaper; there are plenty of others, from free to very expensive...). Enough space on your hard-drive, and a means of easily and regularly making back-ups is essential if you're doing stuff for others. 'Losing' that masterpiece is a Bad Idea. Again, doesn't have to be expensive, but must become part of the routine, preferably before the inevitable crash, rather than later.
Hope this helps.