I'm new to this site and I think it's wonderful! I am going to begin growing a vegetable garden on a site that at one time was a crop field of probably corn. It now is over-grown with weeds and brush. I am going to till the soil and add amendments. My questions are 1) should I choose a low place that can be a bit wet or higher ground that I may have to irrigate somehow in summer, and 2) what exactly should I add to the soil?
Spirit, welcome! Before you add anything nutrient-wise, you should probably have your soil tested. Nearly every town has a state extension office that can give you a soil sample kit and instructions for collecting your sample(s), which are then sent to your state land-grant university's ag department for testing. Here in Tennessee, they'll even email you the results (fast and you can print them off, copy and paste them into a garden journal, etc.)
Fertilizers can help temporarily put back whatever your soil is missing, but if it's been over-farmed in the past, one of the best things you can do is add back organic matter - lots the first year and then a new layer every year - over time, it will not only replenish the nutrients but improve its texture - and organic matter will help your soil strike the right balance between drainage and moisture-retention.