An interesting idea... it could work. Here are the problems I see straight away:
1) Who decides how to dish out the money? Determining if someone is really being harassed is very difficult (due, in no small part, to the subjective nature of the term "harassment"), and deciding if their expenses are true and reasonable is even harder. 2) The main problems with harassment are not financial. It's the hassle, the fear of what they might do next, and annoyance at what they are doing, etc. You can sometimes partially solve some of those problems by throwing money at them, but not to a great extent.
You last type of support - legal costs for someone being sued - is a different matter really. It's a much more obvious situation, so much easy to dish out money for. However, I don't think a fund is required just for that. I'm pretty sure that if I block someone and they sue me, I can just put the details of a paypal account on AN, VP, this mailing list, etc. and get plenty of money pretty quickly.