If’n your ground isn’t frozen have OSU do a soil test

If you have sulphur in your water odds are your going to need some lime

Most veggies like a pH between 6.5 and 7.0

Try this link

Till it up now. Then in early spring, till it again.
15 x 20 is fairly small for a garden, so you will have to limit yourself to your favorite veggies.
Since you’re new at this, I recommend tomatoes, peppers and potatoes. They are easy to grow.
Since this is a small area, I suggest using landscape fabric to keep the weeds down.
Don’t worry about soil fertility. Since it’s a new garden…it’s fertile. You’ll only have to worry about that after you’ve planted it for 5 years or more.
But, if you really want to add something, use peat, compost or cow manure. They will enhance your soil if it’s clay.

you can get some really good gardening info from: ohio state university.. they have a very good website for gardening info… as well as your county agriculture extention agency… check ohio government to find the web address… when i’m starting a new garden area I : cut sod out, till soil, add ammendments (compost, leaves, organic matter), and continue to add leaves and grass clippings every fall
vege gardening is a lot less complicated than it first appears from all the horticulture info
you can also visit my past answers for more info on improving soil conditions.
Happy Gardening!

I’m not sure what the soil is like in your area. if it’s sandy, you may want to add peat moss. if it’s clay, probably compost and gypsum.

Research each plant you select for preferred pH ranges and adjust your soil pH with lime or sulphur (up or down, respectively). A good soil test would be an excellent idea.

A local garden center visit with some of your soil might be a good idea for tips on what to add.

Your question is good with lots of info supplied, but I can’t help much. Sorry!

Good Gardening!

Go to your nearest garden centre they will be happy to answer all your ??? and tell you what is best for your area…