For Vetsulin at least, what I have seen for a rebound test is to cut the dose in half or go to 1 unit, whichever is lower. (Source:
http://www.vetsulin.com/vet/Cats_Monito ... mogyi.aspx - near bottom of page)
I would feed him as much as he wants and not worry about that with the BGs too much. Heavy eating can come with high #s or with low #s - in either case it is the body's way of protecting itself from danger, so I am in the camp of feed as much as they want whenever they want (for a diabetic cat not struggling with being overweight, that is). Yes, it can affect the BG readings, but if they are acting really hungry in my experience it is often for a reason.
Personally I wouldn't worry about switching syringes immediately unless you really want to. You can eyeball 1/2 unit increments on the U-40s, and get U-100s if & when it looks like you really need them. Some people are more comfortable going ahead and getting them, I felt more comfortable using up the syringes I already had and getting at least close to a working dose before tackling the conversion and all that (it's easy, but if you are already stressed it's just one more thing to think about). Totally up to you whether or not to switch syringes at this point - if you do, keep us posted and we can help you figure out how to use them and which ones to order, etc.
As far as the vets, I would do what you feel comfortable with. If the vet is making you feel uncomfortable, I wouldn't bother reporting what you are doing. With my vet I found it doubled my confusion to get her opinion vs. differing opinions here vs. what made sense to me, so ultimately I found it easier to report things to her after the fact. As someone else suggested, you tend not to get as much grief from the vets when you can report good #s and successful results!!! Otherwise they are going to, by nature (since it's their job) tell you what to do, and if you disagree, it makes it more uncomfortable. That was my experience at least - everyone has their own approach, so go with whatever your comfort level is.
As far as the dose, it's pretty hard to tell for sure what is going on (at least it is for me!
), and even when there were apparent moderate results the night of 2/2 on 5u, that could well be that you were shooting through rebound. I agree it makes sense to try 1 unit since the starting dose was 2u, and back on 1/17 that looks like potential rebound already. I would give it a couple days to settle out and see where you are (no more than 3 days tops) on that dose, checking for ketones daily and watching his behavior as well. Ideally you will start seeing more of a U-curve and then can more confidently increase the dose in 0.5u increments every 2 or 3 days. Although I believe the Start Low Go Slow doc (see sticky on PZI forum) says one week between doses, that is very conservative for PZI and generally from what I have seen 2-3 days is all you need on a dose to see if it is working. If not, you raise. Some people like to wait longer (and there's more room for that if the #s are at least getting down in the 200s, then you can be a bit more leisurely with it), but with Bix at least, I generally found 2 days (4 cycles) to be sufficient.
It sounds like you are really doing great so far with all the reading you've done and info you've retained. It's overwhelming at first, but you are on top of things and it will only get easier (antijinx!). 
