Hi welcome to the community.Hope you will enjoy our company.I am trying to answer one by one.
1.Normally buyer pays first.But some sellers have COD arrangement.The disadvantage is ,the buyer may not accept the item.
2.It comes directly from seller.
3.Ebay will send bill to seller around 5th to 7th of every month.
4.Domestic shipping may be 2 days to 15 days normally.
5.You pay to eBay every month as a seller.
6.As soon as you start selling successfully,eBay will cotact you at eBay's cost.You get the number in your mobile.
7.Yes,of course.That depends.
Thanx,
Truly,
Amitava