It looks like they aren't selling kits anymore, but the greasecar web site might be of interest. Their system starts on diesel then after the engine heats up you can switch to used vegetable oil. The engine heat warms up the vegetable oil so it will flow through the injectors. Before shut down, you must switch back to diesel and purge the vegetable oil. This does not sound very feasible for automatic start / stop but it could probably be done with some effort. A water cooled diesel generator would be needed to preheat the vegetable oil. Here's the link to their web page which includes Technical Resources and FAQ sections:
There is also a book about running cars on vegetable oil, "From the Fryer to the Fuel Tank" by Joshua Tickell.
Q9 - As for system design, the generator will create either 120 volt AC or 240 volt AC power. It can be located a reasonable distance away from the batteries and inverter / charger which are normally close together. If you add some PV modules, their charge controller is also typically close to the batteries. This is driven by the relationship between power, voltage and current. For a given power of 1000W, at 240V the current is 1000/240 = 4.2A but for 1000W at 12V (battery voltage) 1000/12 = 83.3A. The higher the current, the thicker the wires need to be to prevent power loss and voltage drop. Higher power systems usually use 48V battery banks for this reason.
My system uses Schneider (formerly Xantrex) equipment. It includes an automatic generator start (AGS) controller. This unit allows setting different generator triggers for start / stop. Mine starts the generator when the batteries drop to a programmable voltage setpoint. As soon as the inverter/charger sees the generator come on, it waits for it to stabilize then automatically switches over and starts charging the batteries. The inverter also passes the generator power through to all the loads. If a heavy load starts the generator may slow down causing the inverter to disconnect it briefly then reconnect. When the generator stops the system goes back to the inverter output automatically. This is all transparent to the loads so computers don't crash, etc.
The generator is water cooled diesel based on a Kubota tractor engine. It includes a start control module which handles all the glow plug preheat timing, cool down, etc. You might be able to use something like it to handle the switch over from diesel to vegetable oil. The Schneider AGS might also be able to do this, it has a lot of options. The AGS in my system just closes a relay to short the start wires together when the generator should run. The inverter talks to the AGS so you can set it to stop the generator with a few different options. Mine turns off when the charger ends the absorb phase indicating the batteries are charged.
Q10 - We are totally off grid and this setup has run without issues for over 5 years using lead acid batteries. I just switched over the LiFePO4 batteries and only had to change the setpoints for charging voltage and the automatic generator start. It has programmable quiet hours when the generator won't run. Otherwise, it only runs when it needs to rather than on a specific schedule. That is probably better for battery and generator lifetime.
As Andrew said, Will Prowse has a lot of good info. Be sure to check out his forum site where you will find lots of good stuff and people willing to help you with specific questions:
Some food for thought: 18kWh is a lot of power to generate and store each day. You'll probably need to run a 48V system with at least a 6kW 120V/240V inverter. A DIY LiFePO4 battery bank of 16 280AH cells can store 14kWh. For maximum lifetime, normally you only want to use less than 80% of that so you'd need twice as many batteries. One set costs around $3,000 if you build it yourself from decent quality Chinese cells shipped from US stock. Commercial LiFePO4 batteries will be a lot more expensive. The water cooled diesel generator I bought should run for 25,000 hours with routine maintenance since it turns at 1800 rpm. The air cooled diesel generators turn faster and probably only run for 5,000 hours. A Lister will probably run forever but I'm not sure about getting 12kW out of one. If you run for 2 hours a day, 5,000 hours is about 7 years. If you get a portable gas or LPG generator for around $1,000 and run it that much it might last 2-3 years before the inverter will stop accepting its power. I'm not sure if a diesel generator will have that issue (declining power quality). A separate AC powered battery charger would probably work OK for longer but the inverter inputs are finicky. Anything you can do to reduce power consumption is going to be worthwhile.