Does your donation system explicitly require the tracking of the various donations?

If not, you can just set up a static address for donors to donate and it would be much simpler. Else, you can consider trying out Electrum. While Electrum is not a full node, you do get the liberty of having full control of your funds and they do have a RPC interface for you to use and track the donations. You wouldn't have to synchronise the block chain at all and there is no need for an excessive amount of storage space either.