Donate button in the sidebar defaults to donation of $5, while in donation page you ask for as much as you as you can as a single donation in order to minimize Paypal's share of the donation. It would suit your preference better if the donate button linked to the page linked in the donation page where you can write the sum yourself.

Then the question: If I donate a sum of money to CF, is it possible to pick the PBF's later, even after months during multiple occasions (Eg. you donate for 5 and pick 3 characters and still have 2 left to pick for later)?