I quit in the spring of 2000 after smoking for 24 years...anywhere between 1 and 2 packs a day depending on the day. .

Here are a couple of observations:
You will gain weight. I think your metabolism slows and you have the urge to stuff your face to squelch the cravings. Even if you keep your caloric intake at the same level as you did while smoking, you will gain weight. This phase will last about a year. After that you will gain and lose weight as you always have.
Just be prepared for that and go with it...don't fight it. I know too many people who were distressed at the initial weight gain and went back to smoking.

There are Internet support groups. As with all things internet, some are better than others so look around and find a group that suits you. They were a big help to me.

I suspect someone will chime in and say they experienced no weight gain, etc.etc. And perhaps it doesn't happen to all quitters, but it happens often enough that you should be aware of it.

Good luck!

Cyril