I agree with Brian 100%.
And, I think you meant charger/inverter, not charger/isolator. If so, there are several ways to go. The best inverter/chargers tend to be from Victron and Magnum. I like the Victron MultiPlus, but there are others. I would avoid Xantrex for anything except the EchoCharge.
Whichever inverter you get, be sure to get a pure sine wave model; they're not much more money than the "modified sine wave" models, and will work in any AC application.
If you want a charger only and a separate inverter, look at the ProNautic series by ProMariner AKA the Sterling ProCharge Ultra. They are first class chargers, affording you "world power", i.e., they can be used with 120V or 240VAC. Really nice chargers and worth the little extra.
For an economy charger on a diesel boat, look at the Iota DLS/IQ4 chargers. A lotta bang for the buck.
Both of these chargers come in several sizes.
Re: hooking up your 12VDC backbone, here's one way to do it which features automatic tending of the start battery -- no need to switch anything (just leave the selector switch in the #1 position all the time). It also shows an option from the #2 position which can be used in an emergency to start the engine from the house batteries. Also, if you study the diagram carefully you'll see that it is easy to isolate either the house bank or the start battery, or to combine all of them if you ever need to.