Tentative “yes”, if you’re literally just pressing a button for another character and can not, say, use one character to manage industry jobs in system X while the character that actually owns them is on the other side of EVE in system Y. However, I suspect that once you impose the required restrictions to make it just button-pressing and not an increase in capability you’ll be left with a system that is, at best, not very useful.
Same for pi. Opening another chars pi set-ups and restarting extractors.
No. PI happens in space where you are vulnerable to attack. This would allow you to have a bunch of PI alts with no ship skills and manage their PI activities with a 100 million SP PvP character. That would be a significant increase in capability, not merely the removal/reduction of loading screens.