I have a number of purchases from Amazon that are from separate vendors using Amazon sales portal, they are mostly one offs... do I list them as separate vendors or just under the main main Amazon account in my ledger?

I see no accounting reason why they can't all go under amazon, as long as you have a record of the actual seller/shipper. Note that there's 3 categories at amazon - sold/fulfilled by amazon, sold by another vendor but fulfilled by amazon, and sold and fulfilled totally separate from amazon. Maybe use a code in your ledger for reference.

Why do you want to complicate matters, if these are completed transactions surely one vendor is sufficient