You better double check. If it were negative film, that would be on the safe side. With slide, that might be ~1/2 stop overexposed, which is worse than 1/2 under.
Nope. My palm has twice the reflectance of a gray card. Opening up a stop above a reading off my palm gives me readings which produce very well-exposed slides. I am careful to get the maximum reading off my palm though, and that is why.
I do use a digital device in my photographic pursuits when necessary.
When someone rags on me for using film, I use a middle digit, upraised.