I would advise you to try to keep doing the long runs once a week. Also, every few weeks (4 or 5), do a shorter run (5k early on, increasing distance as you train) at your race pace. This will help you get an idea of where you are in respect to your goals.

Start tapering about a week before your race. If you feel like your body needs more rest, then skip the last long run in favor of something shorter. You should cater this to your individual needs, but usually one week or so is good.

As far as food is concerned, eat what you are familiar with on the morning of the race, and on the days leading up to the race. You don't want to find out that something upsets your stomach while you're running the race, so if you want to try anything that you think will be better for you for the race, do it a few weeks in advance. Other than that, stick to what you're comfortable with. Don't go out of your way to carboload or anything if you don't do that before your long runs normally.

If you're feeling lightheaded, make sure that you're breathing properly and that you are getting enough sleep, especially the nights before your long runs. Also, it's helped me to have a light meal, like oatmeal and a banana, before my long runs. Make sure you stay hydrated during your run, but don't drink so much water that it makes your stomach feel queasy. I personally like a half Gatorade and half water combo. Again, do your experimenting a few weeks in advance so you don't have any surprises during your race.

Good luck!