Here are the few guidelines suggested by CQ Experts (from google groups):
1. Folder/Asset Naming convention
a. Is it good a have a folder/Asset name contains underscore ( _ ).
Is CQ providing any best naming conventions.
2. Assets (Images/pdf/docs whatever)
a. What is the max size limit of an Asset?
3. What is the max number of Assets that we can upload in a dam folder.
1. Yes folders can have underscores. I didn't see any issue till now.
2. Max size limit I am not sure but I injected around 10 to 30 MB size with out any issues.
3. There should not be much issue even if you inject 100 to 150 gigs of assets. we migrated around 130 gigs with out much issues. In terms of number of assets inside a particular folder (Number of nodes at one level) Adobe recommends dont use more than 200 to 250 at one level. If it is more than that front end DAM UI will slows down (still repository doesn't show any issue)