ocd said:
1.If you can, what horsepower #'s can you expect?
500rwhp is the 'safe' limit of the oem fuel system.
2.How safe/reliable is it?
Very unsafe - even with a weak wastegate spring and your boost controller turned all the way down, you could still boost-spike and run lean.
3.Do you need to use a VPC?
Although you'd make more power with a VPC, this would actually increase your chances of pushing too much air for your oem fuel system. Staying with a MAF might help a bit to keep your boost lower.
4.What aftermarket fuel system is the best to run on the T78 set up without overdoing it?
HKS Rail, 680/720 injectors, -6AN fuel line to 1 side of the rail and oem fuel line to the other side (with fuel pulsation dampener bypass), and 2 GSS341 Walbro pumps. You can buy a kit like this from several suppliers, including MVP Motorsports... Note that a T78 could outflow this system as well - 850cc injectors will be 'safest' (along with proper tuning, of course).