Hi lister-IRL, sorry not to get back to you earlier but my Wife had her hysterectomy last week and I have had to be nurse, cleaner and cook for the last ten days, not a problem as I care deeply for my Wife, unusual in this day and age.
You say that you have a Victron inverter that will be able to split generator power between your home and battery charging. Is this unit a stand alone inverter or is it grid tied? Please post some more details.
Having looked at your control unit, it is only designed to auto start when the starting batteries are getting low. This could easily be converted to auto start once your solar batteries are low, provided you are happy with only 12 or 24 volt storage.
What it won`t be able to do is charge the two separate starter motor batteries. There are several possibilities here: the first is to use the old built in charging circuit that is part of your brush generator head, it`s not very sophisticated and I wouldn`t recommend it as it will easily boil your starting batteries during a long run, if miss adjusted.
The second is to use your main battery bank as the starter bank for your ST2, this has a lot to recommend it, as long as you are able and willing to hand crank the generator into life in the event of the batteries having fallen too low to crank the engine. The possible problem with this is that the control unit will probably continue to send the order to start and send current to the starter motor irrespective of the current/voltage available, this could burn out the starter motor windings, send excessive amperes through solenoids and flatten your batteries even more.
A third option is to have a separate pair of starter/cranking batteries connected to a pair of maintenance chargers driven off the 240 volt AC in your home, this is the option I have chosen and it works well, the starting batteries are always charged and never over charged by the antiquated ST2 charging system. My ST2 generator has never had a flat battery or failed to start since I went down this route, they cost around 15 Australian dollars each and my starting batteries have been faultless for three years, despite my being a tight arse and using very cheap lead acid cells.
There are four stages in the ST2 automatic start up procedure: 1, the demand triggers the supply of current/voltage to the inbuilt starter motor (built into the generator head and triggered through the large contactor in your top box). 2, opening of the fuel rack by lifting the large 24 volt solenoid on the left hand end of the engine. 3, the generator head starts to generate electricity and this is used to release the decompression levers allowing the engine to start. 4, oil pressure, if the pressure is inadequate the unit will automatically shut down.
Now back to your original question, "will this control unit do what I want it to?" Yes I believe it will, provided it is working as an off grid system, running your home and charging battery storage through your inverter. If you are grid tied then that is a completely different scenario which requires a cross over switch between you and the grid to ensure the safety of workers on the electric grid.
More info please,
Bob