I can’t remember exactly but I’ve a feeling even 9 speed MTB rears mechs don’t play nicely with 9 speed road shifters/stis (assuming its Shimano setup).
Wrong!
They play very nicely, shimano road 9 and 10 speed shifters will happily talk to shimano MTB 9 speed mechs, it’s 10 speed MTB (Dynasis) that is incompatible…
Running 1×9 with an old SLX mech, tiagra shifter and 11-32 cassette at present and it’s great, 34t ring at present, which has been OK, perhaps a little spinny on flats/roads so I have a 38 ready to fit.
If you can, I’d look at 10 speed simply because it would give the option for slighty wider range cassettes, if you are going 1Xn…
I am still on the lookout for a decent (ideally cheap) tubeless tyre myself…