I just purchased a VPS with cPanel from SolarVPS, and I'm awaiting the account details. What I really want to know is, is there a way to transfer the accounts from my current resellers that I have my domains spread out on, to my new VPS in one go, or would I have to go through the process of doing it for each domain/site individually?
I believe it would be one at a time. Technically, although you can move all sites at one go if you have the root password of the server you are moving from, that method is most of the time comes with errors and it is better to move one site at a time so you be sure the transfer is done correctly. I personally if that if I got in the VPS, create an FTP account and on the Reseller account use the full backup method to ftp to that account in the VPS and then SSH and moving the .gz files from all the sites to the /home folder and doing a Backup Restore in WHM, it works best even for huge files. Doing the WHM Transfer seems to be problematic if the sites are over 200mb in size. If you do a bulk transfer hitting the 200mb undocumented limitation would bring you a lot of headache. My vote would still be to do one site by one site move, I know it is more trouble but I am sure you want to get everything up and running the first time around rather than finding out after you lose the current host that some files did not go through.
If you have cPanel, it is with just few clicks. In WHM< you can see "Copy multiple account s from remote server" and besides it has 2 other options as well.
This option will only work if you have the root password of the remote server. The OP only has a reseller's account and that don't come with the root password.