Hi!
In short there is two ways to start:
Cheap, action ready system like Fifish, or Gladius from Chasing
Cheap, easy to start working and make money.
Quick learning, but also limited in functions.
Not for surveys or more complex projects.
One way is to start this way and try/learn, upgrade/buy new system later.
More complex open system like BlueRobotics.
Not necessary more expensive at entry, but more to learn and steap learning curve.
Almost unlimited expansion possibilities on the plattform hardware and software wise.
Professional almost like a workclass ROV.
Underwater resolution is seldom the primary camera question.
Its more of lighting for the type of project, field of view, light sensitibility, visibility in water etc.
There are 4K cameras compatible with BR to buy, or build yourself.
Search the forum “4k camera”
Grippers are also unlimited (only budget and weight/size)
An example from forum: