This could actually work. I like it. Though, I think that in order to do the fusion with the Goten & Trunks Buddy System, both of them should be near, or equal in power. Like let's say the transform powerlevel is 1,500,000. Goten is at 1,750,000, and Trunks is at 1,250,000. They wouldn't be able to fuse. I say about a 3% difference in powerlevel, and within that difference, it would be counted as equal power. I have an idea for the attacks for both Goten & Trunks. I think as well. In each transformed state of Gotenks, his time should degrade, to help balance things out. His transformations shouldn't take as long as all the other characters, due to his timelimit. He should either transform instantly, or very quickly.
Generic Settings
Fusion Multiplier: 1.5x
Transform Multiplier (for Goten & Trunks): 1.25x
Time-Limit while fused: 5 minutes
Time-out time: 2.5 minutes
Goten
Starting PL: 600,000
Transform Powerlevel: 900,000
Fusion-Enabled Powerlevel: 1,500,000
Attacks
Basic Ki Attack
Generic Beam
Kamehameha
Trunks
Starting Powerlevel: 700,000
Transform Powerlevel: 1,000,000
Fusion-Enabled Powerlevel: 1,500,000
Attacks
Basic Ki
Generic Beam
Finish Buster
Gotenks
SSJ Transform Powerlevel: 2,500,000
Multiplier: 1.25x
SSJ3 Transform Powerlevel: 4,000,000
Multiplier: 1.5x