Hi Jaynepg
Hedgehogs are surprisingly good climbers, but 8 to 10 inches sounds quite high (depending on what it’s made of, etc.), so I would be inclined to make some sort of ramp, or some more shallow steps for the hedgehogs to get up – a bit more inviting.
Hedgehogs don’t have territories, as such. They have ranges, which overlap. They are solitary animals, so that if (males in particular) meet, one may biff the other and roll it up, but other times they might just try to avoid each other.
Don’t know how big your garden is, but you can certainly put more than one box in a garden, if you so wish. The hedgehogs will choose whether they want to use them or not. Sometimes hog houses get used quite quickly but other times may need to have been in place for a year or two and become part of the scenery, before they are used.