Hi Teal,
I have a J-pouch now, but I had an ileostomy for eight months last year. I was extremely unprepared as there was a mere week between my official diagnosis and my emergency surgery, with symptoms only being present for about three weeks. My family and I basically turned the stoma nurses away when they tried to prepare me for one prior to surgery, because we were so desperate that drugs would work.
This approach does not work, so I'm glad to see that you're seeking some information. It will be a massive shock. I don't think any amount of preparation will remove the initial shock and the following emotional impact of the ileostomy, so be ready for that. My stoma nurses gave me a printed out checklist of how to change the bag so that I could stick it on the wall of my bathroom when I came home. I didn't actually use it at home, but it was a great comfort, so you could consider that if changing the bag is a concern.
I don't know what the deal is in America, but I had a hospital dietitian visit me and she allowed me to ask questions about what I could and couldn't eat, and both her and the surgeon gave me a checklist with a recommended diet for the first 4-6 weeks post-op, as well as some general foods that cause problems. Basically, eat bland for the first 4-6 weeks was what I was told. White bread, white rice, low fiber, no raw fruit or vegetables. After that time period, it is really a matter of personally trying individual foods to see if they impact you. I found for me that pretty much nothing caused an issue, but I never tried eating popcorn due to also having braces at the time.
The Australian government supplies stoma supplies for free, but I understand that you have to pay in America. I found that the bag that the nurses gave me worked amazingly well for me. It was the Coloplast Sensura Mio. It was a one-piece bag. I pretty much only used the bag and adhesive removal spray. Many people find that barrier wipes are very helpful if you have skin irritation, but I rarely needed them.
You will learn most things through experience, but I also found that this site was fantastic for info, as well as a safe place to vent frustration when I was feeling down. Everyone here has been through it, so help is abundant here.
Best of luck, and I hope your surgery is successful,
Hamish