Older PSU limits - PSU Expert opinion required

Hi All, I'm building up a server case (old fashioned Monster Enlite case) into a box for internet connection sharing which has a dual redundant psu set up but which is light on with the +12v rail.

Also only has one +12v rail with no 4 pin square atx connector - but I've tapped into the 12 rail from a spare 4 pin flat molex and used a connector from an old 250w generic psu (which is good for very little anyway). Wires cut, soldered and shrink wrapped.

The box will run a basic S478 board with a P4 2.4 HT cpu, basic AGP graphic card (MX4000), TV tuner pci card and pci WiFi card. 4 hard drives (2 sata, 2 ide), 2 optical drives and a floppy drive. One self powered usb accessory (printer).

PSU +12v rail is rated at 15A only (+5 = 50A, +3.3 = 30A) with a combined max power of 380W (total PSU = 400W).

How borderline do you think this is going to be? (I've used this - http://www.extreme.outervision.com/PSUEngine but it only covers overall wattage).

PSU has a 48 pin interface to the redundancy controller, is this a standard and will I be able to replace these with higher rated psu's?

(Planned use is for data storage from 3 users and a hobby business set up, internet connection sharing for a small network and basic internet, e-mail and tv duties.)

tia and Cheers.