For general advice on cutting dados the Related Q&A is where you should start. The core question can be directly answered using previous Q&A, but I've collected that here for easy access.
My advice would be to use smaller blades and spacers for the arbour you have to keep it simple and reduce the overall moving mass. It is generally fine to run smaller blades in table saws, and some say this is even common when assembling dado stacks.
The reason 10-inch stacks require a 1-inch arbour is because the amount of mass such a stack requires is crazy large, and 5/8ths is probably very close to unsafe operating conditions.
This means arbour adapters to fit larger 1-inch blades to the 5/8ths arbour would probably be a terrible idea. Mostly because it would probably work fine until something sudden and terrible happened involving freely spinning hunks of sharp carbide-tipped metal and table saw shrapnel.
As for an insert plate, it is always recommended to reduce the amount of free space around table saw cutters, but is probably not necessary in the ways most dados are cut. This is a safety item, so use your best judgment. If a larger offcut somehow made its way down the throat and jammed the blade, it is going for a heck of a ride in your general direction. There isn't a way of using dados that comes to mind that results in large offcuts, but (as they say) man makes plans and god laughs. You know your tool best.
You will have to remove most or all of the other critical safety items that came with your saw that manage kickback and so on, and your manual will recommend you immediately return those to service once done using dado sets.