I'm pretty disappointed with my finish time at Tink even though I'm super proud of myself for finishing my first half. I finished in 3:15 something, even though based on my training runs I should have been able to break under 3:00. I just had to weave in and out too much around walkers, and it was really hot at the end and the last 3-4 miles were really tough for me. My GPS had me at 13.6 miles because I had to dodge so many walkers. So now I can't use that as a proof of time for W&D because I didn't get under 3:15.

Good thing I have that 10k in a month!
I would definitely use the 10K for PoT. Congrats on your first half!

What you experienced is totally the norm for Disney races, so try not to let it get you down. They are VERY crowded and you absolutely will run a longer distance than the official measurement. Part of it is thanks to tens of thousands of folks of varying speeds on the course, necessitating some weaving around, and part of it it because the official course measurement is taken with the shortest distance possible - so in a wide, banked curve, for instance, the measurement is taken at the far inside, making its distance shorter than what someone running the outside of the curve would actually cover. This is especially so at WDW, where the roads are very wide. I clocked 14+ miles for one Princess Half, lol! Very, very few folks run Disney races with the goal of a PR because it's exceedingly hard to do.
Just remember .... any proof of time will prob get you out of the last corral.
At least that was the case last year.
Submit everything and update until the last day if possible!
(in my opinion)
I used to think that, too, but IDK... based on reports from last year's races, it might be better to take a chance on not submitting, if the PoT would result in an estimated finish time slower than 3:15. Quite a few folks who submitted slower PoTs were placed in the far corrals, while many who didn't submit proof, but had entered faster estimates, were placed in earlier corrals. I think it's a crapshoot either way, unfortunately.
If I have
MVMCP ticket linked to my account, can I make fastpasses? I didn't even think about the fact that we weren't going to have park tickets, but we will def want to hits some rides during the party.
Based on last year, you should be able to make them between 4p and 7p, but not for after the party starts. The FP system isn't used during the party.