I love the Danger Den Maze 2 with 1/2" Barbs
Your choice for a pump is sorta personal preferance. No one I've heard of has had a problem due to the magnetic field yet. The Danner 500gph hs probably a larger field than the 320gph 1250 Eheim. Although a 350gph Danner has less (lower wattage). The Danners have 1/2" thread so all you need is a couple barb fittings.
As for Radiators I'd also consider a Big Momma, which can be purchased for $49.99 at
www.caseetc.com and modded for 1/2" for an extra $5.00. It flows very well and has the best cooling capacity. The aquacube is also a very good choice and probably much easier to mount if you want to do minimal case modding (but don't kid yourself, you will probably need to cut something and at least drill a couple holes to set up any water cooling. that's why this is DIY).
I had watter wetter all over me and I'm fine (car problems) just don't drink it unless you live in a cardboard box and want a cheap fix.
As for pump power, run a relay from a 12v line to turn on / turn off 120v current to pump. Easy to wire but if you can't maybe come up with something else, I'm not going to be liable for explaining.
Negative case pressure isn't totally bad, but you'll get better cooling if the case is fed good cool air from the front, lowering chance of recirculating warm air. Can't you mount a fan behind the new rad? Other problem of negative is sometimes it makes CD-roms get dirty faster (as air sucks threw them). If you do run with only the back fans, try to block off / cover with tape all openings other than the front rad to reduce recirculating heated air.
Because I use a closed loop system I mix up all the coolant then put the pump in the bucket with intake open. Tap put air then start, once everyting full of coolant, I connect hose from waterblock to pump undre water. No Bubbles. I also added a T to catch the few that hide in crevices and just top up if I notice any.