Hey Matt,
I think you will be going fine the way you described. If I got you right you will use your system in the same way as you would play usual vinyl and then don't send it into a big PA but recording it with your SOUNDFORGE. That's fine.
Some hints:
Use the built-in phono preamps (of the mixer, so plug into phono-inputs) if you want to record audio. In this case the RIAA filter is necessary. But that's the same thing like playing vinyl at a party. Same with grounding. don't forget!
Like done 1000s of times before set entry level of your mixer. Sound has to reach 0dB at the most mixers to gather maximum sound quality without distortion. I hope you have a channel-VU to check this. Otherwise... well... describe your gear. we will check.
Don't use the EQ of your mixer. In case you have some oldies to digitize and want to change the sound you might do this postproduction easily in best quality in your soundforge. This is where you might also apply additional fx like exciter on some recordings. There are nice freeware-fx available out there.
back to the mixer: open the channelfader of the turntable-channel to the max or to approx 80% on the most mixers to get full level on the internal bus. If you have a recording outlet which has fixed level: use this. Otherwise use some other output (like main) and open fader here, too (like describer above for channel faders). And be careful to have turned the volume of your amp down before.
Now adjust the input level of your soundcard so you don't overload it / your soundforge. Soundforge has a nice levelmeter to check the levels. Be sure to NEVER go over 0dB!!! This would cause hazardous distortion which makes your recording unusuable. You can stay at minus 6dB maximum and "normalize" level after the recording and postprocessing in soundforge. The normalizing checks the recording and lifts the loudest peak to maximum 0dB. But to stay safe you might also lift to -3dB instead.
For converting into mp3 check different codecs. The freeware LAME codec is not the very best. This is a good reason to spend some dollars. Check in advance which codecs are used by the different programmes. In most audio applications like soundforge you can choose which codec you will be using. Try a bit and choose the bestsounding for converting into mp3.
For easily tagging your mp3s use "MusicBrainz Picard". It will find most songs and tag them so you don't have to break your fingers by doing it manually.
That's it for now...
By the way: There's an easy to use programme for recording Audio made by MixVibes... "EASYRec"
Cheers...
Ralf
c00l People MV Society 
