well you said it was overheating...possibly a headgasket. That would cause loss of compression and starting issues. Maybe try a compression test
maybe.... people forget that a tensioner really only tensions when you replace the belt.... all other times it's bolted in place and doesn't move..... I actually let the tensioner do it's thing then tighten just a bit more....If you find the timing belt jumped a tooth, you might wanna get a new tensioner.