The Multi is just a display. The Tridata you have powers and receives the data from the speed / depth transducers then displays it and sends it around the seatalk 1 network if fitted.
Functionally identical. You will be able to swap your existing bezel with the new head unit. The ST60+ bezel is slightly deeper so the buttons on the new unit may stand a little proud.
The alternator is running cooler with the Sterling dc to dc charger for a similar output which would suggest the Renogy charger is noticeably less efficient.
I fitted a renogy dc to dc charger last year as part of a lithium upgrade. It failed in the middle of our trip to the Faroes. It ran very warm when it worked. Replaced it with a sterling dc to dc charger. A much smaller unit and runs cold even at max output (60amps). The sterling charger is much...
We have the smaller ZF10m. It has a definite and reassuring "clunk" when engaging fwd and rev. I think this is normal. Your cracking sound maybe because it's new. This thread may be of interest.
Hurth Gear box noisy when changing gear