Hi Elise,
You have asked some very good questions! I'll be honest, it will take time for you to figure this all out! I hope you get some good responses!
As far as parties go, people don't really notice what you are eating. I actually find I enjoy my food more now. I'll just have a little taste of everything.
The one on one restaurant thing can be a little tricky, but there is usually something on the menu I can have. If you are looking to eat "healthy" while out dining, which I know we all should, I look toward the Soups and anything crunchy. I have to admit the things I pick out usually are not healthy, but I don't go out to dinner very much.
We are all different and toleratae foods differently.
I find people are very understanding and have not had any issues. I do find my friends actually feed "bad" for me having to leave so much food. I often do not take a doggy bag, as the food is just NOT the same warmed over, but that is a personal thing.
As far as alcohol, I have had the occasional drink, but not to excess. I will have an occasional glass of wine mixed with club soda, fruit juice, etc. I know this is shunned on, but a few times a year has not hurt me.
Good luck! I cant' wait to see the responses to this great question!