Fogging, if done properly, is advisable for any gas engine and won't hurt a diesel. The problem is some folks overdo it thinking more is better and the opposite is true. Diesels can't differentiate between fogging oil and fuel which means your fogging oil will be combusted leaving you with a feeling you accomplished something when in fact nothing advantageous results from fogging a diesel. Trying to do it manually is futile unless you can somehow ensure you oil each cylinder.
Re: battery storage - wet cells won't discharge so you don't have to charge them "once a week". Perhaps monthly might be more accurate and most of us check our boats at least that often so no problem. Also, it probably isn't worth the price of AGMs unless you already have a charging system which can take advantage of their charging scheme.
Winterizing the water system - there is already lots of info available on the internet I won't reiterate but to say if you are putting antifreeze in your tanks, you're just wasting it. Empty the tanks by pumping and simply introduce antifreeze at a convenient point in the system to the faucets.