Hi John,
Don't worry. I've walked from St Jean to Santiago 3 times, am bursting to go again! You are likely to get every possible type of weather from snow to pouring rain to heavy mud to boiling hot sun; it is all part of the fun and you will be amazed at how little it will bother you. Just take your time and go with the flow...
I wore hiking boots the first time, wore them for part of the second trip, and abandoned them in favour of ultra light running shoes the last time. My choice is now the ultra light running shoes, but my advice is that you should wear whatever you have worn before and find comfortable; forget every one else's opinion. It sounds like you are comfortable in the shoes you use for your race walking, they are tried and tested for you, why change?
Contrary to what one would expect I found that my ultra light runners actually kept my feet drier than my boots - I think because although it takes a while for boots to become wet, it also takes a long time for them to dry. The runners had light mesh uppers and moisture just evaporated quickly. Ankle support is interesting, in light runners I am more sure footed so did not need it, whereas in rigid boots I did sometimes turn my ankle (but was protected by the boot). So both have advantages and disadvantages.
Second point, blisters will not bring your camino to an end. If you know how to treat them they are perfectly manageable - this I know from personal experience. In the first place, obviously, try to prevent getting them. Blisters are caused by heat, moisture and friction - minimise any of those and you minimise chances of getting blisters. Some people swear by vaseline; I haven't tried that but think good socks are just as important as shoes. However, if you do get blisters, they are not a problem if promptly attended to - prick them with a sterile needle as soon as they appear to let out ALL the liquid (which is what causes the pain) - you might need to prick them in several places as the worst blisters are in pockets, but keep the skin intact. If treated properly eventually the skin will harden and form a protective barrier. Change your socks frequently (I take my shoes off, air my feet and change my socks every two or three hours in summer, letting the socks dry out on my backpack and washing them every night).