I created a vendor "One Time Purchase" and then in the Payee field I put the vendor I used for that transaction.

Skip the vendor field completely and just type the name in the payee field. You do not need a vendor number at all. Besides, in credit card receipts if you use a vendor number it creates an AP invoice for that vendor and marks it paid by the credit card.
If you need to edit the amount later when you are reconciling the credit card it will only void the payment portion and the AP invoice will still be there so then you edit the AP invoice and repay it with the credit card. Some people don't realize this and leave the AP invoice sitting out there.
I only use the vendor number if I need to include it in their 1099 or if I want to track their purchases regardless of payment type. Or if it's important to be identified by the vendor number on the job cost records.

I assume you are talking about the Vendor field in the 1-1 Checks screen. But if you use 1-1, you can't print checks from that can you?

Yes you can. If you enter the check as 0000 and save the record then hit print and you will get a check printing window. The system will look for transactions with 0000 and allow you to print checks for them.