Only if you prime it and paint it well and even then, it would not last as long treated ground contact lumber.
No, I would not recommend it, get treated wood.
No, you can not use this for that span. You would need to have at least 2"x10"x20' at an 12" on center spacing. This is due to the load rating. Also if you live in an area where there is heavy snow fall you then would need go to an 2"x12"x20' See the link below for further information. https://www.mycarpentry.com/rafter-span-tables.html
Yes, picked up at store.
189pcs per pallet.
Hi , for this Lumber, if ordered on Homedepot.com, will be shipped and purchased as it is displayed on Homedepot.com when localized to your area. The product price is displayed in bold underneath the name of the item on the product page. We appreciate your business and look forward to serving you in the future. Thank you for shopping Home Depot!
Thank you for your recent inquiry with The Home Depot, Jaynash69. As this is an in-store only item, I believe the best advice would be to partner with a member the Pro Desk at your local Home Depot store for bulk pricing. We appreciate your business and look forward to serving you in the future. Thank you for shopping Home Depot.