Yea, you've got a pretty good handle on it. Any good waterproof (preferably marine) bearing grease will do for the thrust bearing, DuaneHTP can set you up with what he reccomends (& I use) for a non-exotic outlay of $$$
http://hi-techperformance.com/
I personally use 85W-140 in my rear bowl bearings because it is what I use on all my vehicles (Mystic JT-7). I'd reccomend treating both of these after every trip to the lake (or weekend trip anyhow)
The u-joints on the coupler are probably less likely to encounter water seepage than your thrust bearing is but, why not keep it simple and put a squeeze or 2 in them every year of the same stuff.
Vibrations are usually an object (rock,stick, rope) lodged in the impeller/arround the shaft. also causes cavitation which ruins thrust. Dents & dings on the impeller face causes cavitation, reducing thrust and increases RPM. AExcessive gap from impeller to wear ring allows water to flow from the high-pressure section to the low-pressure intake section (blowby of sorts) which reduces thrust. I run a polyurethane wear ring from DuaneHTP and could NOT be happier. Other vibrations, noises, etc, will usually come from the thrust bearing. If it fails completely, your shaft slides fwd to bottom out on your coupler then pushes with hundrede of pounds of force on your crankshaft thrust bearing (can't say enough how VERY BAD this is) so strange behavior needs to be checked out promptly. It cost a guy on the Taylor Boats Roost Board his crank recently, another guy his suction piece as the impeller literally ate it moving fwd.
I am running a Berk "F" with factory trim nozzle which has only been rebuilt 3 times since 1978 ('79 by DuaneHTP, '90, and this coming fall/winter (to match recent engine upgrades, budget causing delay). She has behaved flawlessly other than my digesting far to much sand 1 DAY(!) in '90 and grinding the front 1/4" off my impeller against the wear ring. (The gap should be measured in thousandths, not quarters of an inch) They are a very easy drive to care for and mine has not even had the greatest care in recent years untill it passed from Dad's hands to mine 2 years ago.\
Best of future fun and fortune to you. :clover: :shift: