Just remember to avoid the 10spd shimano MTB stuff - they've changed the pull ratio of the mechs/shifters. Likewise, I've heard the 11spd Shimano road stuff has a different pull ratio so won't play nice with 10spd stuff (would love to be told otherwise, I have some 5800 stuff I'd like to use).
Yeah, same cable pull, as long you use a 10 speed chain.
You can run a 10 speed derailleur on an 8 speed shifter, just need to get the indexing down right.