I don't think helmets obscure your vision, especially when you are concentrating so much.
All good points already been made.
Keep aware of what is around you, if there is something behind you move over and let it past. Ease off, then give chase and see how long you can stick with it.

If you are approaching a corner and something quick catches you, try not to let it put you off, get through the corner as normal, and then move over and let it past.
People (including myself) fluff corners when you have a car right behind you, cause you naturally concentrate on it rather than the corner you are trying to negotiate.

Most of all be relaxed, build speed through the day, check your car after each session, let it cool down on a cool down lap and tick over for a couple of minutes when you have stopped before switching off, don't put your handbrake on straight after coming in (can warp discs).

Enjoy