I haven't got direct experience, only that of my Mum, who needed an emergency colostomy due to peritonitis bordering on septicaemia, from a burst diverticulum. I don't know if she was warned prior to the surgery that it might be needed, it was all done in quite a lot of a hurry as she went into hospital with the peritonitis - but she had it all explained to her afterwards, anyway. She was in ICU after for a while, but recovered well.
She was told that she could have it reversed, but chose not to, as she felt that it wasn't worth undergoing surgery again after the 2 years they'd suggested - she hated hospitals and they wanted her to lose weight for an elective surgery to reduce the risk for her heart.
The actual colostomy - the stoma itself was sore for quite a while but the stoma nurse who used to come and see her was really helpful, had all the goods in terms of disposables and ways to make it less sore and so on. Mum was offered a plug for times when she went out, so that she didn't have a bag with her, but she chose not to use it as most of her clothes were fairly roomy anyway.
She found certain foods really annoyed the system - peas, lettuce and cucumber for e.g. were big no-nos as they made things too gassy.
One thing mum had that you may or may not have, as you have said they'll be removing endometrial tissue - Mum's entire bowel had to be lifted out of her body so they could wash out the cavity, because of the peritonitis, so this broke some of the structural areolar tissue that holds the internal organs in place. What that meant was that when Mum turned over in bed she could feel her innards "slopping about" for a few weeks, while the tissues reattached. But it's unlikely you'll need that done to the same extent!
When Mum had hers, all the stoma services were free of charge, including all disposables. I don't know if that's still the case. Also, your stoma could end up being round or oval - it's important to know the difference because the suppliers cut the bags for you, and if you have the wrong shape hole (happened to Mum a couple of times) then you don't get a good seal and you could get leakage. But you should be allocated a stoma nurse, and she/he should tell you all of this.
Hope that's a little useful to you anyway and good luck with it - it's not the worst thing in the world to live with, but learning to manage it can be not much fun. 