As long as you use exhaust pipe sealant to make sure there are no leaks, it doesn't matter.
I prefer bolted on myself, as it makes it easier to remove if you need to service the system. With welds, if a piece of the system goes bad, you have to cut the bad section out.
It makes no difference as long as whoever installs it, makes sure both ends are sealed permanently.
Depends on the one your replacing it with is.
no.
I live in az and my 90 Silverado has a bolted on cat, does it need to be welded on?
