There really is no minimum distance between the graft and the first bud on a scion. So if you where really skilled at cutting. Each piece of a scion with a bud could be used to graft with.
This is easier with technique’s like chip or T budding. But can also be done with W&T. (although impractically hard)
Some people keep 2-3 buds on the W&T (whip and tongue) so if you want to see how many grafts you can do with a scion, i would go for 3-4 internode lengths. If you cut a little shorter and end up with 1 bud it’s fine to.
If you want to get the absolute most out of your scion’s. I think your best bet is Chip budding (or T-budding, chip is imo “better” though. Can also be done when the bark is not slipping.)
If had scions with only 4 buds that i did 4 successful grafts with. using chip budding. I have even grafted internodes without a visible bud from the 2-1 year old transition. And forced them long enough to grow. (took some patience. And a lot of rootstock buds to break off)
This post i posted before has some nice video’s (not mine) teaching chip budding.
I would highly advise parafilm or similair for chip budding. Although it can also be done with other materials. If using anything else than parafilm (or buddy tape or similar) take care not to wrap over the bud of the scion. (if you wrap over 1 bud of a W&T but it has 1-2 “free” buds it’s fine)
ps: if your first (and only) bud on the scion is really close to the graft union. I would cut of the closest internodes on the rootstock (don’t just knock the bud of, “shave” of a slice including the bud and 1-2 mm next to it)
That way it’s easier to be sure your growing the scion (bud) and not the rootstock. And lessens the need to unwrap graft unions to check.