harvesting composted material and worm casting would be very difficult without modification of the typical lid
tops of the tanks would require significant insulation to prevent freezing
If 2 tanks in series are utilized the second tank would need to be installed with the inlet lower than the outlet of first tank. In order to provide a free draining 1st tank (avoiding anaerobc conditions and providing the required worm habitat) the outlet would need to be at the bottom of the tank. This would result in burying your second tank about 1 m lower than the first.
it would be difficult to control nutrient carry-over into the final greywater discharge to the aquifer as there is not the nutrient uptake that would be performed in a natural wetland system for example
How much land do you have where you are considering your discharge? What are the BC regulatory requirements for greywater and what are your chances of having an inspector stop by?
If you do decide to experiment, consider a backup/alternate disposal option should any system failure occur. Construct all parts of the system so that they can be inspected and maintained.