Hi David
3/16" is the standard size for brake pipes, I prefer to use Kunifer pipe as it is not quite so soft as Copper but that is just a personal choice.
6mm or 8mm should be fine for the fuel pipes, again I prefer Kunifer pipe but copper will be fine.
Not sure what engine you are using but I would probably opt for 8mm fuel pipes.
Both Kunifer & copper pipe is very easy to source from the likes of Ebay or at you local motor factors.
The same can be said of the brake pipe fittings ( M10 X 1 for Ford fitment )
Not sure about the IVA requirements for the support of tubes as I have not done that particular job yet
I am sure that one of the builders will be here with the answer to that one shortly.
Hope that is of some help
