I have a very special little friend who was diagnosed about the same age. Her mum was shocked, then disappointed then relieved and now excited. So you have a lot more emotions to process yet!
Fist point is that ALOT of the questions you asked are very child specific. I will tell you of her experience to help you.
First and most important to her, her aides are PINK! So they are awesome
they really are cute. She adapted to them very quickly. She was amazed at the new sounds she could here and how she could understand everyone talking with little effort.
Her hearing loss was effecting her learning. One cannot easily learn letter sounds if one cannot hear the letter sounds. So her speech wasn't getting better and she was turning shy. The aides fixed that. She talks clearly and is bubbly again. She giggles when she sees me and signs hello Amanda without curly hair. She h two Amandas in her life
she was given a place for one year at a signing preschool to learn all that she missed by not being able to hear. She signs well, and speaks well. Mum wanted her to be able to fit into both deaf and hearing communities in case her hearing degenerates. This year she has joined a regular grade one class, although mum wanted her to do the first year of school she wasn't able ( rules!) so she may need to repeat one year. Wisely they found a school with some support for hearing impaired children. Her mum says this takes a lot of stress off her. She will be able to keep up, it's just catching her up that is tricky.
So some advice. It's your opinion of and attitude towards the aides that will effect her the most. Be excited, be positive they are a good thing! Also in the mean time teach her as much as you can using pictures. Math is pretty visual make sure she finds that easy so it's one less area she will need to work hard at. Also teach her to sign and learn yourself, it's better to have all bases covered. She will spend much time in a hearing impaired community even if she has an aide so better she can communicate to them all.
My friends mum was frustrated often by the delays in getting the aides fitted but says it was the best thing they did for her. I hope your experiences are positive also.