In terms of the HWguy overheating: you need to release your fire button when the bar gets close to the end, let it cool slightly, then fire until it nearly overheats again and repeat. At no point during this time will you actually stop shooting at people, so you're at no disadvantage in that regard. The skill is just to maintain the heat bar at a high level without letting it push over the edge.
edit:
On the subject of rockets, the server you are on makes a fairly big difference. I get a frustrating level of rocket lag playing on US servers (im in the UK), but I don't have too much of a problem playing on EU servers. Its still a little delayed, but its certanly playable. I'm not sure whether this is an issue that the dev team can do much with, but whether it gets improved in the patch or not, its one of these things that will feel increasingly natural the more you play the class.