You should be able to reuse the helm and ram that you have. If you look at skunkboats posts of his re-power he was able to change some of the steering components to get the engines to fully tilt out of the water. If you are going with garmin AP, then get the smart pump. I put one in in 2020 and it has been the best AP I have owned, it will steer at any speed and sea condition I have been in. There should be a market for your old motors provided they are running. When I got re-power quotes included where trade in value of the motors. You can also list them for sale here, other boating sites and marketplace.
The other costs that will come up will vary from boat to boat and how crazy you want to get. Since your engines are off, what does the bang plate look like? does it need to be replaced? or do you plan on glassing over the top of the transom? Since the engines are off, what do the motorwell drains look like. If they are original, you may want to think about doing those as it will be much easier without the engines and rigging in the way. You are going to have your 20-year-old boat apart, and good access to a lot of systems, you are going to find other problems that will need to be addressed. It's just the nature of boat ownership. looks like you already did the fuel lines and the tanks so those are good.