No, this system does not include multiplayer replication. It is designed for single-player use, but it can be extended if you wish to implement replication yourself.
No, the character does not use buoyancy physics. There is currently a function to align the character to the water surface so you could modify it to add buoyancy.
No, strafe swimming is not included by design. The system is designed around forward-based movement with natural/smooth rotation.
Yes. The system is fully compatible with custom animations, as long as they match the expected setup (in-place animations and correct skeleton).
All animations are in-place, with the exception of the dive animation.