Hi Alex welcome back to the bis. From your questions you sound like you sort of know what you are doing so I offer my advice based on my 15 years experience as a DJ.
Here are some answers I hope will help you make up your mind;
1. Me neither but I agree, its good to have the option available. Both Velocity and PS2 can accomodate the need considering they are both equal with scratching ability.
2. This is a matter of personal preference and comfort, for me I don't like buttons so close together and prefer having my decks on either side of a mixer instead of the "on top or below" arrangement.
3. Ok, but its also nice to have a road case/console/coffin for the sake of a tidy setup and ease of mobility.
4. Yes but an all-in-one system can be awkward and heavy to move around, again a matter of personal preference.
5. Just my opinion but a good DJ shouldn't rely on a BPM counter for accurate beat mixing, and shoudn't be a factor in deciding on what equiment to buy. Use your ears, they're more reliable and accurate!
6. See answer #5 also the QMX2BPM is a good mixer but I just don't like its layout and overall feel. You want to choose a mixer that you feel comfortable using, doesn't have to be American Audio brand either, shop around.
7. I'm the type of DJ who prefers the hands on approach over a computer controlled solution. The Velocity/PS2 CD players have a lot more accuracy in all aspects. Because I do a lot of mobile DJ'ing I could never trust a computer to go the distance and handle being hauled in and out of venues, vehicles etc. You should know, based on your own IT experience that computers are never foolproof.
8. CD-R yes; CD-RW no; Try using well known brand names of CD-R, like TDK, Sony, Maxwell etc. Record CD audio a low speeds eg 2x or 4x for best results.
9. Save your money and buy the best, don't compromise on price.
Overall the best advice I can give is to get out to all the stores and try the equipment for yourself, get some hands on exposure and compare all the different equipment manufacturers for yourself. Just because we say a piece of equipment is good for me doesn't mean its good for you. You need to decide for yourself. Good Luck.
ROQ out.