I think just about everything you asked about has been covered but here's my take.
1) What is something you wish you had known before going into the surgery?
I was lucky enough to meet a woman my own age who had the same surgery when she was 10 years old, certainly put things into perspective. She gave me great advice about how to deal with everything involved.
2) Did you have a lot of trouble with leakage? I'm a little nervous about this.
Only about 6 months after surgery when I started to gain weight, my stoma retracted a little and I did have a few leaks, but was all sorted when I switched to a convex base. No major problems since except with the filters which basically don't work, I just put tape over the top of the filter and it's all good.
3) I've heard about rectal discharge, my surgeon mentioned it too, but how much are we talking about? Do people have full BM sized amounts of mucous come out?
I had a panproctocolectomy which includes removal of rectum.
4) How difficult was it for you to figure out what foods worked/didn't work?
Can eat anything and everything (including nuts/seeds/popcorn/fruit/veg/fibre), I don't chew any more than usual or drink water in excess, but I realise I'm the exception rather than the rule in this for most ostomates.
Unlike a couple of replies above I didn't have a nasogastric tube inserted thank God and from what I have heard about this kind of surgery in Australia I don't think that it is standard procedure here. In fact from the day after the operation my surgeon insisted I eat anything I felt like and as often as I liked (which I did and still continue to do 10 years later!).
5) How long until you felt comfortable getting back into physical exercise?
About a couple of months.
6) What bags work best for you? I'm planning on ordering samples.
Have used the same make and model since surgery (Hollister Adapt two piece, convex base and barrier ring).
7) Ladies, any lingerie or swim wear help you feelt more comfortable?
And finally a female answer!
I wear the same style underwear as I did pre-surgery (high waisted/full briefs), comfort is everything to me. My stoma is placed just below my navel to the right, so my undies cover the whole bag and everything is tucked away tidily (?bag what bag?!). I often wear a camisole or singlet under my clothes too which gives a great line (and covers any out of control curves!)
The special ostomy undies are a waste of money in my opinion, the best nickers I buy are from Target (2 Pack Matt & Shine Full Briefs for AU$10), and are incredibly comfortable, fit well without being tight over the bag.
When swimming I just wear a one-piece.
The following Dutch website has some great ideas about clothing and even though the site is many years old (hipster jeans?! - am glad they are no longer fashion), there is a lot of good info about all things ostomy.
and there are groups and pages on facebook that are well worth a look.