Soil:
Does your soil drain well?
Grape vines do not like to sit in puddles or really wet areas.
They don't like for their feet to get wet.
After a good rainfall examine your proposed site area for standing water. This is one of the many reasons why most but not all vineyards are planted on hill sloping hill sides.
Grape vines don't need much to feed on and they are fairly adaptable. Adding the wrong amendments can have a significant impact on your vines.
Believe it or not grapes don't do well in rich highly organic soils.