1) That might be pixels from the bottom of the broken brick texture bleeding over to the top of the polygon. Adrian, you could possibly fix that by either putting a row of clear pixels at the bottom of the texture or making the texture 'clamp' instead of wrap in the .vtf settings. It's hardly worth the time to fix something so minor though.
4) Like markpeterjameslegg said, it's a game design choice not to let you drive the tank. First, it would be hard to code. Second, the map wasn't designed for it. Third, it would totally mess up the dynamics of every game mode. If the tank weren't there though, people would complain about that, too. So I put the tank there as a detail.
5) Since our resources are rather limited, we decided to leave out the dam as a playable area in Dam. Torn focused on taking the other part of the map and adapting it for multiplayer. So being unable to get past the gate is not a bug. If you were able to get past the gate, that would be a bug.
