Note that you could very possibly make this more convenient by making it node-based. Make a node for each town/city/port, and connect them via the roads. You could put extra nodes between where necessary to simulate longer marches. (Not that there's anything wrong with a hex-map, but you might find it easier to make node maps).
That map is probably plenty large for 8 players. I remember seeing an AAR on it or one of the comparable maps with six, and I expect it could easily handle two more. Bear in mind that the DBA standard is something like four territories per player, plus one in the middle. That would be 33 territories for 8 players, and this map has 100. The more territories you have, A) the longer the campaign will take, and B) the less often armies will run into each other.
Not bad ideas, but I’m hoping multiple armies per person and relatively large movement allowances will help with that. We’re gojng to sim out a campaign to see. But we can try something out with the border princes map too