To enlarge on Havoc's post just a bit concerning publications, I would add "Electronics for Vinyl", also by Doug Self. Published about 5 years ago, it has lots of detail, good explanations, and some circuits that might be at least partially what you are looking for.
There's no real answers to those queries. In general specific op-amps are not generally preferred for particular functions.
It's really all about the signal source and the output requirements. So looking at impedances , load etc then select/optimise op-amp parameters based on those.
Summing Amplifier - look at existing designs. You won't go far wrong with a "classic" NE5534 or better solution (esp as I think NE5534 are now EOL ?) but you need to look at bus resistor values and mixing topology - eg unbalanced / quasi-balanced / balanced to optimise the whole thing.
And for a non-inverting (eg a simple follower or non-inverting gain stage stage) you should look at CM distortion.
