You'll probably get better responses then mine, but here is my take
1. no, you push the throttle and more water is forced out the rear giving you more thrust. The time to plane is very quick, I believe it is in the 3 second range. There isn't any other control over trim.
2. I believe the Yamaha engines should be among the very best in terms of longevity. Mine is only 40 hours old at this point and i don't have any issues. Since there are less moving parts in the jet setup, I believe it should be more reliable.
Some things to note, and as I said, others can weigh in.
1. for fishing, you would want a trolling motor, does the FSH come with one? If not, it is easily mountable? On my 192 there isn't an easy way to mount a trolling motor
2. Yes, the jet boats can go shallow since we don't have props to hit bottom, but in weedy terrain, you can suck up weeds through the bottom of the boat which would cause you to have to stop the motor, pull a plug in the transom area and pull the weeds. If you fish in heavily weeded areas this might be a concern
I think the pros are they are easy to maintain, reliable and quick to plane
The cons might be they are more gas hungry than a similar sized prop boat? The potential for weeds to be inhaled into the jet system.
Lastly, if I had to do it over again, I would go larger, but I would stay with the jet boat. I love not having a prop (for the kids) and I absolutely love the design. Make sure 19' is enough for you. They might come out with a 21' or 24' fish boat next year. (I have no idea just guessing)