Setting up a SMA SI6048 battery backup / AC/DC coupled / grid tied system (DC Solar trailer)

I'm new to posting here, and thought everyone might be entertained with my project.  Thanks in advance for your input and advice!

I brought home a DC Solar trailer a couple weeks ago.  Fun road trip out to Vegas and back to MI, feel bad about the gas, oh well, only way I know to get all this stuff together for a decent price.  Everything on it worked as intended, we'll see how the FLA batteries hold out but I'm optimistic so far.  I'm adding the components to the house.  There will be a lot of that happens in stages.

0.  test and unload the trailer.  complete.    Pictures:   https://photos.app.goo.gl/qbVKkST35cJAB9Zc9
1.  put the SMA SI6048 inverters on the wall in the garage (unheated, in SE Michigan).  put the batteries underneath, build a box with venting (and heat?)  charge from the grid and equalize the batteries as a start.
2.  set up rack and panels from the trailer outside in the garden.  ground the panels together to a ground rod there at the garden.  likely put a breaker box at the panels, then 150 pvc conduit to the garage and set up the Midnite CC, with the breaker box from the trailer.   charge the car from it when it's sunny or the batteries are full.
3.  connect the SMAs to the grid, and to the house.  couple questions here
4.  later, make it so the roof micro-inverters can connect to the AC1, during weekend off-peak, to charge the batteries and run loads in the house.  During on-peak weekdays, the roof system will go completely to the grid, and the battery/SMAs/DC coupled will run the house loads.

Background:
We have a roof mount micro-inverter 4.7kw solar, that goes to the main outside service panel on one end of the long ranch style house.  We generally don't use a lot of electricity, and the rooftop solar system matches the annual load on the main meter.  However, we have an airsource heatpump water heater on a separate meter, and have added an electric car recently.  Part of the motivation for the trailer is to start added more solar to handle those extra loads. 
From the outside service panel end of the house into the basement original main breaker panel is about 40 feet, and the main breaker panel will become the new critical loads panel, fed from the AC1 side of the SMAs.    I'll leave most of the house circuits there, except a couple of high load items (AC and car charger EVSE) will move to a new grid only panel, also with a 30 or 40a breaker feeding the AC2 side of the SMAs in garage.  It's about 80 feet out to the garage.   
The garage is about the only feasible place to transport 2 tons of lead, so the batteries and SMAs will go in the garage.   For the near term, the panels from the trailer will go outside in the garden.  Longer term, maybe I'll add more panels on roof with microinverters AC coupled to the SMAs AC1 and the house loads.

Questions:
DC panel grounding, do I need to connect the panel ground 150' away to the main house and AC system grounding?   The DC charge controller at the garage will be grounded there at the house.

Battery box heating, am I likely to need a heater?  I'm thinking I might?  But maybe good insulation and gravity venting only will keep it warm enough?  What should I use for a heater, or will they stay warm enough with an insulated box and up/down during the week with full charge from grid every week or so?.

Connecting between the main panel out to the SMAs in the garage and back again, 80 feet away, how do I want to do the grounding and neutral?  Do I need to run neutral and ground in both directions between the basement main panel, to the garage SMAs, and back to the basement critical loads panel?   
    -Ground would be bonded between the grid and the critical loads panel there in the basement and the ground rod right outside there.  At the garage I'll add another ground rod outside. 
    -Should the neutral be connected straight between the grid panel and the critical loads panel, or only route out to the SMAs and back?
    -The run from grid to SMA AC2 doesn't need to be huge, I will have a smaller 30-40a breaker in the grid panel, this will only be to charge the batteries at some constant reasonable rate, at night or weekend off peak,  or only enough to match the average load of the house.
    -Maybe I want this new grid panel to have a pair of linked breakers as a manual transfer switch, to run either out to the garage and back from the SMAs to the critical loads,  or just straight to the critical loads (also disconnecting the AC1 return from the SMAs in that case)
    -The SMAs can do 56a 11.5kw out continuous, and higher for short times, this will meet any of the house loads, especially after leaving the AC and EVSE circuits only on the grid.      The run back from the SMAs AC1 I would use #6 copper L1/L2/N and G.   Neutral in the SMA is continuous through the AC1 & AC2 ports.   That N line would need to the same size, so maybe I just convinced myself.  All I would be saving is a smaller #8 or #10 wire going out the garage.  

Well,  just writing some of this down has helped.  Please let me know what you think.   Thanks!  

Dale