Only up to £5000 pounds, and as far as I am aware, we would be handling much larger amounts than that. So as a temporary measure to get membership fee's etc tax reimbursed would be fine, but it wouldn't work during the annual fundraiser. For that, the charity registration would be necessary.
Yes, precisely, but we can wait until after we've got the £5000 to worry about that (which eliminates the need for the foundation to give us a starting donation). You only have to register in the tax year in which your income goes over £5000, you don't have to have registered before then.