My DD was born profoundly deaf, she's 6, has cochlear implants and her spoken language is above average for her age .
She had hearing aids as a baby/toddler, we had problems with her taking them out when she was small but by 18 months she was fine with them. There was certainly an adjustment period, once we got aids that were loud enough to make a difference to her, where she seemed more tired and irritable but it didn't last long.
We went through a few sets of hearing aids but that was down to finding a set that suited her (she's very profoundly deaf) and then being able to swap for another colour. I think we managed to actually break one set. I guess you'd have an ongoing expense of having the ear-moulds made, DD needed a new set every month or so at about that age, my friends DS was having them made every 2 weeks - it all depends on how fast they grow.
We did some pretty intensive auditory verbal therapy with AVUK to help with DD's spoken language. She had age-appropriate speech by the time she was 4, which was pretty good going considering she didn't get her implants until she was 21 months, and she had heard very little in the way of speech sounds with her hearing aids. DD also had speech and language therapy (mostly pretty useless TBH) and a teacher of the deaf (also pretty useless). She also had full-time one to one support at preschool, although only for a year, when we moved to a new nursery she managed fine with no additional support.
We home educate now so I don't have much experience of dealing with schools, some HI children use a soundfield system, some use an FM system. Some need additional teacher of the deaf support to make sure they have heard everything, some don't. I know when DD was younger there was talk of her being prepped for lessons, so if a book was being read to the rest of the class she'd get a chance to go through it with her one to one beforehand to make sure she could follow it later.
Sorry for the massive essay, there's a lot to deal with when you have a child with a hearing impairment. I hope some of it has been useful.
You could also check out the NDCS they have loads of information and also a very supportive message board if you have any questions other parents might be able to help with.