I'm a support main who really needs to get used to the other lanes and, as he is a tank with decent damage, poke, and sustain, was looking to see if Tahm Kench could be used as a way to ease my way into being in top lane. Does anyone have any thoughts or advice they could share (both on using Tahm in top and what someone in top lane needs to be doing)?
I think that Tahm Kench is good top, and that you need to use his W to poke instead of his Q. When you use his Q+W combo on a minion, it will only use the mana cost of Q, and the cooldown of W as well (so 150 mana isn't used, just 50). I would suggest getting a RoA and then going tanky after that. Anyways, he is quite viable top, but the ins and outs of his gameplay need to be learned in order for him to be viable. hope this helps!
It"s viable, but understand that you still need to build him tank.
E is nice sustain and protection from all-ins.
W can do a surprising amount of damage, even in lane.
Q can be decent poke.
R gives about the same global presence as a 
.
Personally, I would start 
to eliminate any lingering mana issues, give a good chunk of AP to poke with, and get some HP to make the sustain on E better. After that, go for HP to make him tankier and do more damage. You'll be the team's tank, but still do a surprisingly high amount of damage. Think a bit like 
here.
