Here's what I'm thinking. Pull all of your gear together. Get a clean 5 gal. bucket, a bit less than 20 L. Stuff you gear in the bucket. Then you'll have a good idea of what size panniers/bikepack stuff, you'll need. Ortlieb has very good panniers, Nashbar adequate. I know nothing about bikepacking stuff, but would like to know more.
Send me somewhere for bikepacking info please.