I wouldn't worry about the starter. Its such a heavy duty item. That is one car part that I've never had fail on any car I've owned. As long as you're not letting it turn over for long periods of time without the car starting it's not something to even worry about.
IT'S ALL WRONG TOM! In all seriousness it's a good thing to do if you want to do it like that. We would pull the fuse on our hondas to stop the fuel pump. It's how we built up oil pressure before we started it up when we had new built motors.
When you grind tungsten on a sander that's been used on other metal you'll embed all that trash into the tungsten. Tungsten is considered a consumable. As you weld little microscopic pieces will get into the weld puddle. Depending on how serious the job is... especially nuclear. Those...
As long as the belt sander you're using is for tungsten only you'll be fine. I approve of a dedicated tungsten grinder.
It's good practice prep your parts and treat every weld like it's going to be x rayed.
Ahhhhhh keep practicing with the aluminum. Make sure everything is clean when you weld it. Get some scrap and get to work! Butt welds and t joints. Practice practice practice! I tig weld aluminum for a living. Its one of the harder metals to weld but once you get the hang of it you'll love it.