You have given suggested some good measures which will prevent the buyer from doing a charge back. But there are some issues here:

1) If you receive large amount of money as "friends and family" option, PayPal may block your account. That option is not for selling digital items.

2) Also as you are selling digital items, if the buyer makes a chargeback, it will be in his favor. If you do not pay back, you will loose PayPal account.

Thus, it is better to use any other payment option for this. Escrow is best.