I am going. May 8 to May 13. Probably a bit early in the year in training terms in reality but has got me out a bit before France at the end of June.
I only have a road bike with clip-on bars, I think looking at profile that there is quite a lot of the course where TT bike would go well. Cannot recall what was favoured on the video. I do not think you can take gas canisters on the plane. At most places there are track pumps but I will probably take one.
I have used ready made since I started about 10 years ago. I have a -8 for one eye and a -7 for the other which are about 0.25 off my prescription. They are not perfect as I also use varifocal and have an astigmatism, but they do the job for open water swimming. I do not find it too much of a problem in the pool, although as someone does point out it can be tricky to read your watch if the numbers are small.
I get mine from Vision express who have been very helpful over the years. They, at least the last time I bought locally, also sell the lens individually.
I am sure you will appreciate the benefit of being able to see better in the water.