I bought stuff using Paypal since early 2000 and never had any issue.
I will answer your question this way:
The owner is selling it via PayPal, and I'm unsure how trustworthy such a transaction can be.
-Paypal is great to use, if something goes wrong they have protection.
Will there be a postage tracking number?
-It depend what shipping method you or the seller is using. I usually like the Priority Mail. It offer tracking number and is cheap.
How long will it take to get to me?
-Also her it depend what shipping you or the seller use. The seller is in the US? If he is in the US, with Priority Mail it will take 6-10 business day.
What recourse do I have if the seller flakes?
Paypal have protection. You can also ask the seller to list the model on Ebay, on buy it now. So you also can have Ebay protection.
What sort of questions should I ask the seller before sending money?
-Ask them what shipping he is planning to use and if it has tracking number. If he can list the model on Ebay, buy it now.
Good luck! I hope everything goes well!