I would keep the main lift the same. If you look at the very wide variety of things Wendler has recommended, they nearly always (with few exceptions) keep the big four the same. It is the supplemental and assistance work that changes. So, standard main lift for the 5/3/1 sets, followed by 5x10 trap bar or whatever.
Probably not. You will likely have to take a bit of time to sort out the weight. Maybe work up to a 5RM with trap bar, then use 50% of that (recall Wendler's principle of starting light) as a start for your 5x10 work. See how you do with that, and increasing in future weeks as appropriate.
Probably not. I would again recommend finding your 5RM, then use 50% of that as a start.
Seems legit. Personally, I just stick to dumbbell rows, chins, and horizontal/fat-man rows, basically just changing things like weight and rep ranges. It does not seem to be a big deal.