First of all, welcome!

No, it isn't too late to get her a companion. You may want to consider getting another female. You won't have to deal with the neutering/joey issues and they tend to intro better. Nothing's guaranteed with any glider at any age, sex,etc...Sometimes it just doesn't work out. What is important is that they are similar in size.
No garlic, onions, raw lima beans, excessive soy products, chocolate, anything high in sugars, salt, fats and/or preservatives.
It is possible she will never let you hold her. It's rare for a glider to allow someone to do that. You'll find that she hangs out on you though. You have to get her nails clipped. Your vet can do it for less than $10. She should have a well check anyway. They can hurt themselves badly if they get stuck.
She should not need a bath. They clean themselves and should keep clean. If you do need to get something off her, use a washcloth and warm water but dry her off quickly. Anything with harsh chemicals will be a risk to her. You can wipe the cage down daily with hot water. When it needs a good cleaning, you can take it outside and hose it down or wash it with vinegar and water inside.
Don't worry too much about her aim being a little off. Some of mine are that way too. They just get up and keep going. I don't know why some misjudge and others are darn accurate but I'm sure she's OK.
Don't be afraid to ask questions. Read through all the posts on diet, housing, bonding, etc... There's so much info!