I had large medical expense last year. I paid various bills using large sum of gift cards. I have copy of original bill and some of them receipt of payments as well. I have few questions

1. Typically I do not get statement in use of giftcard(like credit card). Is payment proof must or copy of bill is fine ?
2. How long can I wait for reimbursement ? Is there any limit to that ?
3. Since payments are to hospital and various doctors, do I have to claim all individually ?
4. Is there any benefit in waiting for reimbursement(except that fund can grow further) ?

Thanks in advance....