I wouldn't think much smell from a welder, but I usually use outside. Paint fumes linger longer. A grinder is fairly high frequencies, which dissipate fast over distance. They might be loud next to you, but barely noticeable far away. That is why you can tell how far away a rifle shot is, close is a sharp crack, changing to a distant boom. Safest to have sheetrock on the ceilings and walls as a fire barrier. You would spend a lot more money heating a shed for human comfort and/or find reasons to spend less time there. I have a 2 car garage, but prefer doing big jobs like pulling an engine or tranny outside (backyard driveway) because more room to work and better light, but then we have 6 months of guaranteed no rain here. But then I don't officially touch an engine or tranny since Sacramento County forbids any major automotive work on your own residential property, even inside a garage. You can legally only change brake pads or such. I should report myself to sleep better at night.