Q.Amount and type of fertilizer
Father in law used to garden pretty big. Old age prevented him from gardening previous 5 yrs. He has since died. Now his wife and me want to garden this year. Hoping I can get his tiller started 🙂 What supplements should I add to soil when turning over in April?

You may not to add anything to your soil.
A soil test is the best way to start your gardening venture.
Your local County Extension Office can help you with a soil test.
Here is a link to find your closest office.
https://www.gardeningknowhow.com/extension-search/
After you have the soil test results you will know what your soil may need as far as amending it.
Here are some links to help you get started.
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/testing-soil.htm
https://www.gardeningknowhow.com/edible/vegetables/vgen/starting-vegetable-gardens-guide.htm
https://www.gardeningknowhow.com/edible/vegetables/vgen/vegetable-gardening-advice.htm
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/improving-garden-soil.htm
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/too-much-nitrogen-soil.htm
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/what-is-organic-material.htm