I think the suitedness and slight connectedness of the T7s makes this speculative rather than marginal so you can open it from MP.

http://en.donkr.com/Articles/plo-from-scratch---part-2-208

This guide is a classic if quite old. It might be well out of date now, but it's a good starting point.

As for calling a 3 bet I'm really not sure.

Yes and Yes. Run the equties on http://www.propokertools.com/simulations. we need 33% to make the call and if he has 2% (aa only) 3bet we barely not get the odds but then the implied odds go up and also his range is face up and we can win on tons of boards with the worst hand.
Vs more normal 3bet of like 5% we have 40% eq and need to call.

This is definitely a call pre, especially in position. As for the preflop open, you could maybe fold this from MP at the beginning of your PLO journey (if that) but it's a mandatory open from CO even if you want to stay on the tighter side of the force.

I wouldn't be potting this UTG but it is a matter of preference. This hand plays to overset people. The T7s is not really that much. It looks like more than it is. I would likely be making it like 12c rather than pot. This lets blinds in with trash and you want them to call wide and play oop. It also reduces the pot size for likely calls where you are oop.

K89ddx is gin but if we get it in the T7dd just blocks their combo runs.

In examples like this hand if we open EP smaller and get 3b the 3b is small and we call call with a higher SPR which increases the value of hands that play to overset people.

If I had a suited run I would pot UTG as getting 3b isn't as much of a big deal as it is with realistically shitty kings.