When playing Start From Scratch, you only have $500,000 to begin. With even the cheapest field on the map running at $102,624, it's obviously important to pick a good field to start with.
First we have to determine equipment costs. After testing, I've determined that harvesting 1 field will not pay the lease cost on equipment, so we will be buying our equipment instead of leasing.
Italicized items are for grain harvest, underlined for corn/sunflower and bold are for baling. Normal text indicates it is used for either application.
I picked the Fortschritt HW 80 over the Strautman SEK 802, even though it's slightly more expensive, because it has more than twice the carrying capacity as the base model SEK 802. To get the same equivalent capacity in the SEK 802 would cost $11,000 (halfway between the 8k and 12k capacities)
In case you're wondering why potatoes, beets and cotton are not on the list, it's because the starting equipment for those require more than $500,000.
This eliminates all but 8 fields. 3, 15, 16, 17, 18, 21, 22 and 23.

• Field 3 is the largest at 5.04 Acres. In fact, at first it seems like a great deal, at only $295,342, or $58,609 per acre. But if you buy Field 3, you can't afford the baling equipment for a while, so the best harvest you could hope for would average $14,091 on Canola. The first harvest of Oats will only bring in an average $7,141.
  
• Field 17 is the next largest with 4.76 Acres. For only $213,912, or $44,939/acre, it's actually a better deal. First harvest of Soybeans will bring an average $13,237. And it's cheap enough that you can afford baling equipment for an average 2nd harvest income of Wheat at $22,324.
  
• Fields 15 & 21 are the third option, with a combined total of 5.7 acres. Per Acre is $48,117. However, combined cost is $274,272, which doesn't allow for baling equipment. First harvest of Canola and Wheat averages $14,954. Best 2nd harvest on Canola would average $15,937
  
• The only remaining option worth considering is Field 16. 3.61 Acres at $137,904 or 38,200/acre.
  Sunflower crop would bring in 1st harvest average $10,144. Best 2nd harvest would be Sunflower at average $10,144.

I referenced Undying29's Guides Field Sizes and Cost and Crops Yields and Prices for field sizes and costs as well as harvest incomes.