A0 is probably a drum scan
A1 you could get away with a very good flextight scan from a good operator
you can ask Genesis where they recommend for each
You can defo squeeze A0’s from a Flextight. I have two at work and have blown medium format stuff wayyy bigger than A0. 35mm film is a little trickier, anything less than 100iso and the scans will be graintastic, but very very usable.
Ordered some. While I've got you, where should I send 3/4 negatives to get pro scanned to be printed A1/A0?