Dear 00,
1. Realworld scenarios always surprise us. Assume you are in the product detail page and the session was timed out after 30 minutes. Now, if you click the confirmation page, then confirmation page is the first page of visit and it is captured as entry url/page. Same goes if you route the customers directly to the page using any deep link or SMS link.
2. There are plenty of resources related to this in Adobe Community, please search and go through. Look into my blog as well whenever you get time.
3. Make sure that your implementation is good and fine. If yes, your data should be okay without big anamolies because it is by-default dimension for any prop and if the implementation is fine, everything should be fine.
Thank You, Pratheep Arun Raj B (Arun) | NextRow Digital | Terryn Winter Analytics