Hi Jaek_3,
Not withstanding possible PSU issues (and you should be OK with that additional MeanWell unit), the startup delay with "the works" installed could potentially be due to hardware initialisation or RAM check delay. Same goes with your choice of GPU - I never had success with an ATI Rage 128 in a TAM (and 5500), because of driver conflicts with the onboard ATI Rage IIc. In fact with these two cards installed I could get acceleration on one card with driver switches, but not both. I'm tempted to try a Voodoo 2 or 3 PCI card next to avoid the incompatibilities.
Going onto PSU issues though, I can confirm on a completely recapped CC with G3 (no additional power apart from 1A 3.3V regulator for PCI), it doesn't take much to tip it over in terms of power draw. I had to install a 2.5" IDE HD in mine to get it reliably booting with a USB 1.1 PCI card, anything more (PCI VGA, full size 3.5" HD), it wouldn't boot.
Lastly, point a desk fan at the internals with "the works" installed to rule out overheating, does your CC have an additional fan installed on the side of the case? A common mod was to cut away at some of the shielding and plastic internal skeleton to install a relatively high speed 80 or 90mm fan inside. With G3 + GPU it will overheat using the stock fan.
JB