I can only mention 2 of your questions. Hope I help. You should be able to run your headphone mixer regardless. I ran a cheap headphone amp/mixer out of Audiobox USB as I took the signal right from the regular headphone out and into the amp/mixer I put. It works fine for me.
As far as professionalrecordings, you'll find that is very subjective and depends on your use of the audio. Audio for Cds is obtainable from almost any current interface on the market. What costs money, is the preamplifier and the # of inputs you need to run simultaneously. If you are recording a band and a lot of inputs all at once, it's gonna cost you. If you are an electronic based outfit or will only need to record 2 tracks at once (not that you would have only 2 tracks, but how many you need to record at the exact same time) you can get started with a 2 or 4 input interface for a lot lot less. If you are gonna record 5 mics on a drumset, and enjoy whole gang with 10 tracks on one take....your gonna pay. I FIND more than not, new acts over buy and don't really record the way they think they would. Theoretically you can record a whole 4 peice band on 2 inputs on a Audiobox 2input usb interface and get a great product. If you're gonna do film work you'll need more. If you're just starting recording find a way to watch a session recorded live and talk to an engineer who has only a few years behind them. Better yet, watch YouTube sites like Produce Like A Pro(my fav) or The Recording Revolution. THESE guys are perfect for what you wanna do. Audio interfaces cost more than most computers you'll need. If you like Apple, most music engineers do but you will pay much more for your software forever!!! Use what you got. Money no problem, I love MOTU as its dependable.Start small &grow when you know what you need for sure. Stay away from know it all started and audiophiles as they will make U part w/unessesary cash. You'd be suprised what you can do with stuff you might have and Ebay bargains and a few good pieces. Your needs will change very fast and it sucks to be stuck with stuff you can't return. You can make recordings with the cheapest stuff made today and it will still be 1000 times better than the Beatles BEST recorded album.!!!!!! Think about it that way....
All the major companies make good enough stuff today. It's not like the old days anymore. Even junk is better than to pop the line 7-8 years ago. Your absolute best bet on tech questions where the answer will cost you- is to go to the manufacturer site, like Presonus and register with them and ask their techs in writing ad get a written answer. You won't have 1/2 the hassles then. Good luck I hope this helps!!
