I recently started to level a monk first as windwalker but then I felt like windwalker is the most boring specc I ever played since vanilla....not even arcane mage, hpala and frost DK can be as boring as WW monk for me.
I respecced into brewmaster because healing isn't my thing and I noticed that BM monks are quite OP on lowlevel just like every other tank and I wanted to make him a twink anyways.
70 Twinking:
More players
Could play arena
No PvP gear for Monks so I would have to pve gear with resilience gems which puts me at a disadvantage
More abilities such as healing sphere and ox statue
Less OP tank scaling on higher levels(?)
60 Twinking:
Easier to gear up (Rogue T3 from BMAH)
No resilience so no disadvantage as a monk
No arena so could get boring
So I'm kinda unsure about what level I should play a brewmaster twink for mainly pvp.
I'm faaaiirrrllllyyy certain there's not much information in the way of Monk twinking... There hasn't exactly been much time to figure out that information!
So my suggestion would be to try twinking at 60, see how it goes... Then if it doesn't work out, you can always level to 70 afterward. Can't do it the other way around.
I'm afraid I can't help further. It's not something I really consider.
"Healing Sphere" and "Grapple Weapon" aren't learned until levels 64 and 68 respectively. If you twink one at 60 you'll be lacking the class' disarm and spammable self-heal of the DPS and Tank specs.