Before I had my ileostomy, I had repeated rectal prolapses that were surgically repaired. It wasn't for cosmetic reasons - they made it very hard for me to have a bowel movement, and of course all the diarrhoea made the rectal problems worse. I also had a lot of tears in the skin.
The problem I had was that the surgeries were only ever a temporary fix - I was prone to prolapses, and of course the skin quickly tears again also, if the causes of the problem aren't fixed. One of the many benefits of having the ileostomy is that I don't have any of these things to worry about any more. That was very much addressing the causes of the problem - although perhaps not something to be entered into lightly!
I was very fanatical about keeping the area clean. I'd shower following every bowel movement. I never had any skin irritation or infections, so I believe my attention to hygiene was not wasted! Definitely pay attention to cleanliness - though I'm sure you are already.
You might well find that haemorrhoids and skin tags come back again, so having surgery might result in you going through a lot of trouble only to have the problem reoccur. I do know that haemorrhoids can be removed with fairly minor procedures like banding, not requiring general anaesthesia. The best thing is to address the cause(s) of the problems - basically anything to reduce the amount of strain the area is exposed to, so anything that reduces diarrhoea, or reduces constipation if that's an issue for you - but I'm well aware that's probably easier said than done.
I'm not sure whether surgeons would consider operating for purely cosmetic reasons. I'd assume that very much comes down to the individual surgeon. And then they'd have to take into account issues such as risk of reoccurence, the effect it's having on your emotional state, and risk of complications such as infection.
I can't advise on the sexual issues, as I'm a straight female, but I do recognise that that deciding whether to discuss your sexuality with a doctor must bring up a whole load of worries. Many rectal problems can be assessed by a doctor without needing to go into details of sexual orientation or activity, but I think I'd give you the same advice I'd give to anyone - find a doctor you trust. Most people will feel some embarrassment having a rectal examination, or even just discussing it, regardless of sexuality. I have always felt comfortable with my colorectal surgeon. He never makes me feel embarrassed, and he's examined me many, many times! (Not anymore; now he examines my stoma instead!) So if you can, find a surgeon you get a good feeling about, and, if you can, talk to him/her for a while first about your problems in more general terms, before deciding what further information you feel ok about sharing.
I would recommend seeing a colorectal surgeon rather than a gastroenterologist, unless you already have a gastroenterologist who you want to stick with - or see both; I actually see my colorectal surgeon and two different gastros. at the moment! You're in the UK, so you should be entitled to see a consultant for each problem you have. I don't think your GP should object if you ask for a referral to a colorectal specialist, to address the specifically rectal problems, even if you are already seeing a gastroenterologist for the more general management of your Crohn's. On the NHS, you are also always entitled to a second opinion, so don't feel like you have to go with the first consultant you see. You don't need to have a major reason for objecting to a consultant, you can just tell your GP that you'd like to get another perspective, or simply say that you didn't feel comfortable with the first consultant you saw (if that does turn out to be the case).
Having an understanding GP is always a useful thing too, of course, as they're the first person you have to explain your problems to in order for the referral to a consultant to be made in the first place. You could perhaps even ask your GP to put the basic, medically relevant points of your concerns about sexuality in the referral letter, if that sounds like an easier way of doing things?
