All your questions answered in a categorised manner below.
You require an import/export meter which your power company will provide for you. This counts the amount of power that you will import/export. The exported power is credited to you on your power bill. In New Zealand, this is the 'on-grid' compliance requirement. We do not design the system for you to be making money off your panels by exporting back to the grid, but you will naturally feed power back to the grid if you have excess (e.g. long summer days where you are at the beach and your house is powered and your battery is full - the excess has to go somewhere!
Savings vary from home to home but check out this page to find out more - https://ecoefficient.co.nz/what-do-i-save/. For the life of your loan, solar can be a cost neutral decision and your monthly repayment can be close to what you are saving! Once your loan is paid back you’ll save even more. Of course, every situation is different so please get in touch for a free quote.
If you are a family of 4-5, a hot water heat pump will save you about $1,000-$1,500 per year on your power bill – approximately the same amount as the repayment. This means that for the life of your loan, installing a hot water heat pump can be a cost neutral decision and your monthly repayment will be close to what you are saving! Once your loan is paid back you’ll save even more. Of course, every situation is different so please get in touch to get a free quote.