1) If your gallery is in tack folder wise on uploaded media and your database tables are in tact that held the gallery you should be fine on an upgrade.
If you do a new install vs. upgrade the photos will have to be added again.
The images are stored by userid on the file system.
EX: images for userid 101
2) Photopost Pro and vBGallery are 2 different products. You only need vBgallery.
3) If you are in the records from the transfer I do not see a problem on upgrade cost. Shoot an e-mail to firstname.lastname@example.org
with your details and inquiry for more information.