1. Does a Sony gift card work or does it have to be a Sony Connect card?
Only Connect Ebooks Card
2. Apart from the Sony Connect gift card, which other cards are acceptable?
3. Are any of these cards available to overseas residents?
4. Can I gift a person credit with a non-US credit card?
I don't think so.
5. Anyone else got questions, thoughts, tips, etc on this?
You can buy the Ebook gift cards in the US when either you or someone you know travels to the US. Some airports (EWR, IAH, MIA, etc.) have Borders stores. Or you could ask someone in this forum to buy them for you online. There are some people who've offered to do this for those living overseas.