MIG welding is the norm. No they are not stress relieved.
NoIs the fuselage especially the lower longerons oiled or not ?
As the owner of an experimental aircraft you can do any repair, modification or maintenance you wish. You will need an A&P do the condition inspection (similar to an annual on a certified plane) for an amateur built experimental.If I were to buy a used kitfox requiring some tube replacement can I do that or does it have to be done by an A&P mechanic?
You can do any of the covering or cover repairs. The blanket method is what is used on these. I know of no envelopes available. The blanket method is easier, anyway.How about recovering? Can I do that? I can check with PolyFiber and see if they have envelopes for the kitfox. But if not, can I get envelopes from Kitfox for the older models or do they just cover using a blanket method?