1.I am assuming a user can purchase a file in one of two ways: (1) publically without registering on the site. (2) Or by registering on the site first, then clicking a buy button?
Answer: Yes, that's correct. You can turn on "require registration option" if you wish.
2.I am assuming then that for the non-registered customer who buys an item, they can re-download the item from the link they get in an email or from the thank you page (if they bookmark it)?
Yes, that's correct. They can redownload when back from paypal OR from link in email delivery OR from "My Orders" menu item that you can add (for registered users). If they bookmark it's ok, they can redownload updates if you allow but until they reach downloads limit or hit time expiration limit (not available in screenshots). All links are unique, impossible to spoof or guess.
3.I am also assuming that if they register after buying an item that they will not have any order info to review and re-download after logging in, that this only is made available if they register first then purchase?
Yes, that's correct, but it's a good idea.
4.Is the paypal transaction number available in the orders' list in the backend?
Yes, it is available.
5.How does your secured downloads work that prevents others from using the download link of someone else? There is no info on how this is done (prevented); someone could pass on their download link to others.
If they pass the download link to another user, it will work until download limit is hit (default is 3) or until the link expires (you can configure how much it will last, it recognizes strings like "1 week / x weeks, 2 months / x months, 86400 seconds etc)
6.What is the URL for the PayPal IPN to be entered at PayPal?
URL in PayPal can be yourdomain.com, QuickSell tells IPN URL to PayPal everytime, this way you can use it on multiple locations with one paypal account.
7.What is the Verify Transactions setting for and how is it used?
This setting (when on), after IPN arrives from paypal, the component makes a new connection to paypal and uses their API to verify the transaction number (that it's real not spoofed), last time I checked only my product was able to do that.
8.I also need to be able to edit individual settings of how many downloads a person can have instead of just global for everyone...is this not possible? I was able to do this from Trinitronics product.
Right now there is a global configuration for this, but setting it per user is also a good idea.