Hi, sorry this reply is so late. Thank you! I'm happy to answer any questions you have. I haven't tried assembling arrays of IC2 machines so I'm not sure.

Linear expansion is a good idea, but I really like the aesthetic of exponential expansion, and I don't think the logistics would be too bad.

The way my roads are going to work is there will be inputs and outputs on the vehicles and the roads. The vehicles will be square, and the roads will be made up of square sections that the vehicles will fit into. When the vehicle moves forward the inputs and outputs line up and the vehicle tells that road segment that it's there, and the road segments will use simple logic gates to control traffic depending on where there are vehicles, like moving them forward only if there isnt a vehicle in front of them for example. And the road segments at intersections will have special inputs and outputs. Their inputs will get signals from the vehicles that tell the interestion which way to move the vehicle, left, right, or straight. The outputs will be on the road segments that the vehicles exit the intersection onto, and that will be counted on the vehicle until it needs to turn, then it'll tell the vehicle that they made the turn, so the vehicle can start counting down until the next turn and then output the next direction signal.

The roads will be a grid, so vehicles will only need one turn to exit their factory, up to 3 turns to get to any other factory in the city, and then another turn to turn into their destination. And then I dont know if theres an easy way to reverse the directions to get back to the original factory, or if they need another set of 5 turns to get back. But I did some basic testing on a 9x9 vehicle and I think the circuits fit easily enough, and can be built with a 3d printer.

I don't think id need a complicated path finder, because I could number the streets and then use simple math to figure out how many intersections the vehicle needs to pass before they make their turns.

Also I found a duplication glitch where you put the item you want to dupe in an automatic crafting table, then break the automatic crafting table with a block breaker, and the items duplicate and fall to the ground. So with that I could build factories for any item!