As soon as I could I grew mine back out. Not scratchy or hot for me and without my beard I look like I'm 12. Hard to take myself seriously without a beard.
Shave. Respirators, no matter how good or what type will not seal if you are not clean shaven. It's even an OSHA requirement in industry. Had to let a guy go because he refused to shave.
The spline style will not slip or strip. I'm also in aviation, never had any problems, frequently have to use my spline stuff on bolts others have mucked up. Plus you are prepared for when you do run across the occasional spline bolt.
Depends on the tool. My Atlas Copco stuff doesn't require any, the Cleco and IR stuff says it does. Read the manuals, follow recommendations. Or not, either way.
I've gota Pelican 0450, it's my heavy road trip box. And I do mean heavy. Fully loaded its 90 pounds. Unless I absolutely need it I just grab my tool bag and the exact tools I need for the job. It's a hassle.