question

Thank you @JohnC, much appreciate your input.

For 1) In that case I might opt for the VCC 12-50 (B2B). The old sterling AB1280 was able to pull out up to 40A from the alternator for years, but can't be configured properly for the Lithium setup. That's why I'm looking for something that comes close to the output.

For 2) So how to switch the MPPT's and B2B off in case of a high or low voltage event (not to forget about temperature), when I delete the two battery protect? I thought I could use them as a relay. That is the main question of my initial post.

For 3) The main switch in the diagram is already installed, but too weak to handle expected high currents from the Multi. I forgot to plot another into the drawing. But I get the point.

For 4) That is interesting. I've spoken to a Victron dealer at the Duesseldorf boat show. He told me that I still will need the DMC, even though I contradicted on my experience last year when I disconnected the DMC and controlled the Multi through the remote console within VC. That's why I put it in again.

For 5) The main reason for the separated thruster battery is this article by Matthijs. Currently the thruster is powered by my service battery bank. But according to the article that is not the recommended way in a lithium setup. I very rarely use the bow thruster and if, then only for a few seconds. But it's there, so it will be used. Wired by 8m (count that twice, then it's 16m) of 70mm2 wire. There is quite some voltage drop and that's why I thought it would be smart to put one of the older VRLA into the bow directly to the thruster. Cool, never thought of the Cyrix. That could do the trick.

6) Yes. The diagram is only a first draft to estimate what I need, what to order and what to drop. There is a lot of stuff installed already on the boat.

edit: I read through the VE.Bus BMS manual and discovered that the Orion has a remote on/off, which could be controlled by the BMS charge disconnect. Unfortunately both MPPT's don't have a physical remote on/off. So that requires either a VE.Direct non-inverting remote on/off cable or a BP to control them via the BMS. I'd opt for the BP then to keep the VE.Direct free for connection to the Cerbo. If I didn't read that wrong, it will answer my question.

FYI @JohnC,

Update to 4/

From the Cerbo GX manual I just learned that in a VE.Bus BMS System a DMC is mandatory.
Remote On/Off/Charger or Current limit needs to be set by the DMC. When the VE.Bus BMS is connected, the remote switch feature for the Multi is automatically set off and can't be changed. That's sad, because I was so much used to this feature. But on the other hand it's not really a big deal and is the price one must pay for when going for Lithium.