Question Looking for help evolving my current system

I was recommended to come here to this forum by a rep at Signature Solar for guidance and advice on a proposed modification to my system.  I posted this same thread (with slight modification here) on a DIY forum using the same title, but have gotten no feedback at all.  I'm here for some guidance from technical pros on this build concept.  

My current system is not DIY and was done through an installer out of the Charlotte area with PTO 9 March 2023. It is grid tied with interconnect agreement and has 2 Tesla Powerwall 2s for backup power. Solar is 23.36kW DC nameplate utilizing SolarEdge optimizers and two SE7600U inverters feeding a combiner that then feeds the Tesla Gateway 2 through the disconnect seen to the right of the TEG in the picture below. That TEG feeds my Span Panel that distributes to all my sub panels and loads. It is 400A service with another disconnect to the left of my meter that feeds a load center in my basement. That load center has a generator interlock on it that is actually fed by my Span Panel via a 50A circuit. Not pictured below (but included in the schematic) is an apartment sub panel.

This is a great system overall other than paltry storage for my family's uses. 27kWh is barely enough for overnight in the heat of summer or dead of winter. We need more storage and adding Powerwalls is just not the solution I want to go with. I was planning to go with a Gridboss and 3 Flexboss 21s to I could keep UL listings and all that other stuff, but that doesn't help with one of my other big beefs. That is that Duke is penalizing me for the size of my system to the tune of $49/m minimum because my DC nameplate is above 15kW. It is costing us even more when you count in the other tariffs/leafs they tack onto my bill that are calculated base on nameplate rating.

So here I am approaching the issue differently and looking to get some feedback. This time I'm looking to make it an off-grid system and not worry about UL listings and such. I still want safe and stable though. Now I'm thinking I can build slowly if I take steps to buy off-grid inverters and batteries and expand over time. This would allow me to move circuits to the new build while maintaining my utility connection, but dumping the interconnect and going back to standard Residential ToU. I wouldn't lose the capacity of the Powerwalls at all, since they can charge my 48VDC batteries. Sure there will be extra conversion losses, but I at least get paid to leave the PWs connected to the grid with the VPP (Power Manager - Battery on the bill).

So here is a schematic of what I'm thinking involving 3 12000XPs and stacked, paralleled 48VDC batteries. I'm eyeing the Eco-worthy PowerMega 314s right now. Green items are new for the most part. It isn't full detail, I'll need to dig down in and figure out fuses and disconnects along the way as I get closer to buying equipment and building. I do have one of the 200A load centers on hand though (with the Eaton breaker) that was replaced by my Span Panel. Why 3 12000XPs? We have sustained 25kW load a handful of times and I want my wife to be able to "do what she wants" without having to pay that much attention to her power consumption. I would move the SolarEdge inverter (AC Coupled) output from the combiner into a Smart Port on two of the 12000XPs. I am fairly certain I read they are limited to 62A and combined I max at 64A.
[IMG] removed link [/IMG]

There would be two transfer switches to allow me to connect the grid directly to my Span Panel again. Otherwise the one off the TEG would be to feed a Chargeverter (probably the Eco-Worthy version) or multiple of them. This would allow me to tap into the Powerwall storage when needed and allow my utility rate plan to be a ToU where they only recharge during the cheapest period. This concept would create the division to ensure the utility doesn't logically tie my off-grid system to their utility forcing me to maintain the interconnect.

When Helene came through here a few years ago it really hit our area hard. While I had a better power situation than my neighbors, it highlighted how paltry my PWs really are in the grand scheme of things. With that, this is what is coming to mind right now that I'm trying to accomplish with this proposed build and what I'm trying to overcome:
Ability to add addition storage myself as desired.
Reduce fees to Duke and stop giving them my energy.
Ability to "easily" add additional solar to my system.
Ability to charge storage with a generator.
We intend to add a well and that would require more power than currently consuming.
Redundancy should something go down, I don't lose it all.
Tight Home Assistant integration REALLY wanted, but not a deal breaker.

Current problems:
We can't survive winter without the grid. We just don't generate enough and need grid support from about mid-November through late February.
Current storage capacity isn't able to manage our loads when both HVAC systems are running to maintain heat or cooling during the high/low points.
Nothing can send power to the TEG that isn't CT'd and handled by a certified installer. This means I can't chance anything back feeding the circuits connected to the TEG and must island everything from it or pull only.

With all this (and I know it is a lot), what feedback do you have? Is this doable or is there something I'm completely missing? Any different equipment you would use for my stated reasons? I'm not married to the batteries or inverters, I just know the 12000XP can handle the AC coupled solar and I'm not going to deal with warranty issues by removing the optimizers and such.

My initial plan is one 12000XP and a 314Ah battery (probably Eco-worthy PowerMega) to feed my 240V sub panel that is currently fed by the Span using a 90A circuit. I figure with 100A passthrough, I can wire the 90A from the Span to the first 12000XP and that sub panel to the load side of the 12000XP with the battery. Then Span can shed the load when our PWs drop in capacity below our SOC threshold but the panel would stay powered while it has power in its battery. Ultimately, the 240V sub panel would be moved back under Span Panel though.

One question brought up by the rep at Signature Solar was how would a third (or fourth) 12000XP handle not having solar at all and only run off the battery back to provide power to the combiner?  That would be on the latter side of the phased build, but until there is any solar feeding it, it would only be powered by the battery bank.