My Setup... All Opinions Welcome

Hi, my site that allows my members to setup a marathon profile page so that their friends and family can donate to them when they are running a marathon.

I need to store the donations (maybe in my PP account) and then pay the charity (who are already set up as charities on my site) if the person completes the marathon.

I also need to be able to refund all of the donators if the person decides to refund because they cannot run the marathon

1 - what type of paypal account should i set up

2 - what fees do i have to pay when the site receives donations from donators

3 - what fees does the donator have to pay when they are making a donation

4 - what fees are required when i need to refund all of the donators

5 - what fees are required when i need to transfer all of the donations to the chartiy

I am a little confused how i can manage the donations for each marathon user, so any help at all would be greatly appreciated, thanks in advance