We got our list from our WP's assistant- she emailed it to us several times prior to the wedding- It will have all the info, resi #, check in/out date, what hotel...
One thing to know - if your guests are using DVC points or a Disney employee discount, they will not show up in your room block unless they are added manually. We couldn't figure out why some of our guests didn't appear to have booked when they told us they had. It turned out our WP's assistant had to add their reservations to our block by hand.
The reservation line can not tell you the exact room as those are not assigned until closer to your date. What they can tell you is who booked and what their reservations number. All you need is the reservation number for your welcome bags. Carrie is correct if they book out of the block for whatever reason the reservation line for group reservations will not have that information. You will have to get that from your guests.