Galvanic Isolator
The item you are asking about is actually called a galvanic isolator. An exerpt from a website explains what it is for. "Installing the Galvanic Isolator between the AC safety ground and DC bonding system (see diagram), blocks a majority of the low voltage currents and corrosive action on your zincs is significantly reduced ( while the integrity of the critical safety ground path is maintained.) This means a significant savings in boat haul-out fees and zinc replacement costs."Depending on boat, and therefore anchor size, an electric windlass is a good idea, but in my opinion is "nice to have". A manual windlass would suffice on a 30 footer.If you plan on having and using a fair amount of electronics, refrideration, chartplotters, etc., then upgrading the house battery system is a very good idea. If you use more than one house battery, then all house batteries should be of the same type, size and age (new together), so now is the time to upgrade or wait until the first ones wear out. I would also highly recommend a battery monitoring system like the Link 10. In this way, you know how much "juice" you are using and how long it is taking to recharge. Never discharge batteries below 50% capacity or else it will severly shorten their life.Sounds like you will have a well outfitted boat that you will be able to use basically year round (depending on local conditions). By the way, what do you mean by "side rail openings"?Good luck and enjoy, Bavarias are pretty good boats.Tom