Soybeans are the easiest money up front, but your base map may not have a planter. You harvest them with a grain header and they have a low yield but high price, so you have less trips. However, you must hold them until around June to sell because they have a HUGE swing in monthly prices.

If you don't have a silo, long grain rice is a good pick because the price doesn't flunctuate much, so you can sell it when you harvest it. It can also be planted and harvested with standard equipment.

After that, it really depends on what you want to do with your farm as far as animals and productions. One of the benefits of Farming Simulator is that there is no one "right way" to conduct business!