There are usually a few cheap pieces of land around your starter farm and those help bring the income in with more crop to sell. I also tend to buy land in the beginning. Grass harvests are pretty complex, but you'll learn all the different pieces of gear to get them into bales and sell them. You learn what you need for potato and sugar beats, and cotton. You get to learn the other systems cause they'll make sure you have everything you need to do the job. Which is another good point of the job offers.
You will almost always have to rent the gear. I've turned a 50K+ profit on them before.
Those fill up the harvesters and trucks so fast, you end up having to do a lot of work running back and forth to sell, but the payout can be pretty good if you want to take the time.
I tend to avoid the potato and sugar beat ones.
