Water new trees once a week, regularly, during the first season, with l0 gallons of water. More for large trees. Pour the water down the trunks so it goes into the root ball, not along the top of the ground. In addition, whenever the leaves droop down or it is very hot, water again and mist the tops with the hose. Do not fertilize the first year.
Welding inside of a shop or garage can create fumes. But they can easily be removed from the area by using industrial-type fans, or you can make your own from a recycled forced-air furnace fan. Check with the installers in your area for used fans; the cost may not be more than about $25, or they might even give you one. Cover the intake and all moving parts with heavy metal mesh, and run the power cord through a switch for easy on-off control.