Right then, the Tamiya connectors can't handle anywhere near the power you're trying to put through them, they will melt and create havoc. The Losi connectors look good, but not sure what they are exactly. Deans or similar would be a good bet.
Cheap welded nimh stick packs (if thats what you're using) with weedy wires - again probably won't be able to provide the juice needed. Something might well give up. A decent lipo pack with quality connectors pre-wired would be better able to cope but you'll need a lipo charger of course.
3.5 motor is more than I'd ever use. I did try a mamba max setup with 11.1v lipo - probably somewhere comparable to the motor you're trying to use and my blackfoot was absolutely uncontrolable. I mean, not even funny - it couldn't even get to half throttle it was so insane.
That 3.5 really isn't suited to the blackfoot at all - try a 10.5, should be plenty fast enough and then some.