did you use grease to stick your exhaust crushwashers in? If so, it can smoke pretty good the first couple times until you burn out the grease.
When you stripped those bolts, did you strip the bolt or the holes, and if the holes, were they helicoiled? 'tight enough" usually seems to be when you hold the wrench with one hand, practically right over the socket and tighten down until it stops, then give another little bit with just your wrist. At least that's how I measure it. (things break when I use the end of the wrench...
)
I've screwed up in about every way imaginable, so I have adapted decent diagnostic capabilities and a healthy fear of touching anything.