im not sure if i would plant next to a motorway, not soley on the problem of the plant being highly visible in late summer but more so on the fumes from the vehicles. I think in this climate 500g per plant could be acheived if you got the right strain and a good spot and just basically did everything to perfection, however i think most people end up with less when growing outside in uk. As for pests its probably inevitable that you will run into problems but if you have alot of plants in a few diff locations some may suffer from pests but i geuss you could let nature take its course and still end up with a harvest at the end, however if it was me id definatly try to treat bug probs.