The Powerwall is a neat product, but you still need power input, be it solar or grid,etc. They're infinitely better than lead acid batteries, that's for sure. Higher initial cost, but the capacity is way better, the useful life is way longer, and they don't need the maintenance. There's a ton of info online.
As for capacity, you can stack them. I wouldn't think you need 60kWh unless you plan on fully discharging your car before recharging it (plain stupid) but more battery is good if you can afford it. At my house, were EV only,and we use around 11kWh daily. You just need to be honest about your driving habits.
Charge times are dependant on what you set your charger to. If you want to pull 7 kw out of a battery system that can only supply 2.2 kw,it will trip a circuit breaker. There is nothing on the market that I'm aware of that will automatically de-rate your charger current.
Next up, reverse current flow. With the Bolt in its current implementation, the answer is NO. When we do see this, I have a feeling that it's going to come over the CCS port and the inverter will be in your garage. It's a tentative feature in the CCS 3 spec. Doing the grid integration on the car is probably more responsibility than car makers currently want. But who knows. If there was a grid inverter in the car, the current EVSEs might be able to deal with return power, but I don't think any current spec supports it.