Instead of 1 SOK 12V 206Ah battery you can get 2 SOK 12V 100Ah. Put them in parallel. Now you have a max continuous discharge current of 200A instead of 100A. Now the batteries will support up to a 2000W inverter. The 2 100Ah batteries are only a little larger than 1 206Ah battery.I do understand that the system should be designed to load requirements. Space restrictions limit the design to one battery, this system will be in a Toyota Sienna minivan

It's important to understand power usage. You need to work out how many watt hours per day you need.The largest current is a 900 watt coffee maker which would only run for about 15 minutes, second largest is a refrigerator that is yet to be purchased but since they cycle on/off it appears they only draw about 60 watts per day.

A 900W coffee maker that is used 1/4 hour per day uses a total of 900W x 0.25h/day = 225Wh/day.

A fridge might run at a 20% duty cycle meaning it's on 20% of the time and off 80%. Let's say the fridge you get uses 60W when running. This means in a day it uses 60W x 24h/day x 20% = 288Wh/day. Put in real numbers when you know them.

Do this for all of your items and add up the total watt hours per day and you will know how much you use.

If you go with 2 12.8V 100Ah batteries then you have 2 x 12.8V x 100Ah = 2560Wh of battery capacity. But really 90% of that since you won't use 100% of the battery each day.