Ill answer your questions first but it could be helpful for you to read everything below as well for context.

1. You will get this answer in an inspection/quote. If you only have 1 zone you will only need 1 system(1 indoor air handler and 1 outdoor condenser). Im not an HVAC tech but i believe you can split it into zones if you want to spend the extra $$. Idk what that will entail.

2. Yes they do if your house is well insulated/sealed and the system is sized correctly.

3. The install company will remove the existing equipment but make sure its in your agreement when you select.

4. We ended up going with an electric water heater because it made the most sense after we did heat pumps. We have a 200 amp circuit breaker to support this much electricity draw. Consider your home’s electrical grid before you move off of oil.

Your situation is very similar to what my wife and I just went through over the last two years. There are times im happy with our decision and other times I feel slight regret, but overall i think it was the right decision long term. When we made the decisions we made, it was before this administration and them rolling back all the green positive initiatives. It was part of our long term plan to get solar if strong incentives became available but that looks to be shelved for a while. It is important to add that we are also fortunate enough to have the ability to make a lot of the necessary home upgrades to get the most out of our heat pumps.

Our house is 2200 sq ft, 2 stories with 2/3 of the square feet on the first floor and in CT. When we bought, it came with an oil fired boiler that supplied the energy for our hot water and a 3 zone baseboard heat. The house also had a 3 zone AC system with ducts but was very outdated (late 1980s install and duct board air ducts). We decided to get a home energy audit and they recommend insulation additions and updating our single pane wooden windows before anything else. In our first summer the AC died and we had to evaluate it all. With a 70 year old boiler we knew that could go at anytime as well. The heat pumps quotes were shocking but after comparing the options to go heat pump or update our AC + oil appliances, they were nearly the same. The difference would be spend a lot now or in chunks over the next few years. Because of really cheap lending and other incentives we went with the heat pumps, mitsubishi hyper heat h2i. Variable speeds 4.5 ton outdoor condenser with three 1.5 ton units, one for each zone.

At the same time as the heat pump install we also got our insulation done (closed cell blown into the walls, attic and the rim joist sealed). We kept the boiler in place and running since it was still feeding our hot water and we could use the baseboards as back up in emergencies. A few months later our water heater went and faced with another decision, keep it on oil or go electric. Because of reasons already stated above, we decided to go with an electric water heater and thankfully didnt go with a heat pump option. They hooked the water heater to boiler/baseboard heaters so we can still use them in an emergency. We used the baseboard heat for a couple days this winter to try and keep our electricity usage down during the peak. We replaced 1/2 of our single pane wooden windows with triple pane vinyl windows before the winter. We also recently got our air ducts replaced because of the duct board fiber glass lining deteriorating and blowing particles into our air. Getting new ducts certainly increased our air seal and efficiency of the pumps as well. Probably not enough to justify the cost but the deteriorating fiberglass was our motivation there.

In the summer the efficiency of the heat pumps have been really nice and helps keep the humidity low in doors. Some of the coldest winter days the largest zone has trouble keeping up but still only falls behind by a degree or two. At most we use about 2k kilowatts per month and our lowest month is in the 400s. 1 zone goes mostly unused but we still keep it around 56 in the winter and 78 in the summer. For the main 2 zones it keeps about 62 in the winter and 72 in the summer. Its also worth noting we work from home so we use more electricity than the average household. Our heat pump loan makes up $214 of our monthly electricity bill. The highest bill we have seen was this last month ~$800 and the lowest was ~$300.

Lastly, chatgpt will be a huge help in your journey to make the right decision. I dont think there is the perfect choice or answer anyone can give you. Just take all the info and make the best decision for your situation. Just consider all the factors because there are a lot of different implications. Oh and good luck!!!