1) What discipline on the rune priest would best compliment this list, and why?
Telepathy, Psychic Shriek has won me over as a Primaris and Invisibility is definitely worth rolling to see if you can pull it off. I haven't given it much playing just yet, typically I went with Biomancy as it can really buff the Psyker. Iron Arm, Warp Speed, and Endurance have always helped out my Blood Angels and Imperial Fists.
2) I notice a lot of competitive lists I've looked at seem very repetitive (e.g nothing but grey hunters and razorbacks with some long fangs). Is it possible to win in the current meta with a more varied list?
I don't play in tournaments, but I'll wager this is because if a unit is worth taking once it's likely worth taking twice....or five times. I have found myself successful with more varied lists with all my armies (and I do play to win, after all) but without any real experience at tournaments I hesitate to go further on this.
3) Any general tips on the list above?
If you've got games coming up in the next two weeks it looks solid (though I don't play Wolves) but I'm pretty sure there's a new Codex coming out very soon considering the model releases for them. Might be worth waiting on finalizing anything if you haven't yet concocted this list out of grey plastic.