You can ask if you can delay it. In theory, so I've been told, the ideal envelope between surgery and chemo is no more than 10 weeks. The longer you wait, the longer any random cells left after excision have to do their dirty work, If you are going to push that envelope to the max, which happens to some of us for reasons beyond our control, you would need to have a frank discussion about the risks which will become a bit more obvious after you get the results from your clearance. Not that you will get a definitive answer given the whole uncertainty about the disease and treatment, but if you want to go, ask.
The weird arm feeling and swelling is very common. Having someone puddle around in your armpit doesn't do your circulation--lymph and otherwise--any good and there are a heap of nerves in there which also come out second best in the tussle with the scalpel. If you have access to a lymphedema team--nurse and physio--its a very good idea to get in touch with them early. They can take some baseline measurements so you know in future if your arm is getting bigger or if it is settling down. They can also show you how to do some massage which is designed to help clear any extra fluid. We all get given a hand out with the exercises on it, but having someone take the time to show you is much better. Mxx