Well as for restaurant repair most of your work will be done at night after 7pm
where abouts is your location? I was a chef before a welder.I dont know of any certs to get you in the door. All you really need is a good under standing of what your doing the material that you'll be working on mostly and getting your foot in the door. most chefs like myself are picky about your apperenance
if you look professional chances are I hired the right person that means
when asked a question you dont spit and sputter over your words like aa or hmm I dont know ,I guess so, most chefs that you will find have no sence of humor.We take food very very seriously.

There is a few places over here that build there equipment but no one portable not that I have heard anyway.Anyway these places dont care if you are certified or not if you can tig and I mean really tig then all you need is a chance at the right place because word of mouth travels.