The recommended recipe for a square foot garden is 1/3 compost,1/3 peat moss, 1/3 vermiculite (garden grade).
You can use composted cow manure but you might want to mix it with regular compost as it might burn the plants if too rich.
The top soil would be a good mix.Make sure you water well because the peat moss soaks up all the water.
Refer to your planting recommendations in your area to set your plants out.Too soon and it will frost on them.I go by Mother's Day in Ohio but our weather can be tricky and sometimes I wait a week or so.Ask you local nursery.
You need a special soil for your seedlings.It has to very light and airy.One bag will be all you need or you can use
those peat circle that you add water to and they swell up and you add the seed.Make sure they don't dry out and water only from the bottom.You just drop these into the garden after the plants start to grow if all threat of frost is gone and the soil is warmed.