Our average last 32 degree frost here (10% chance) is April 28th. I like to wait until early-mid May before putting out tomatoes, because the ground temp is warm enough (above 60 degrees), the air temp is consistently (and rarely below) in the upper 70's by day and 50's by night. The weather is normally coherent with those planting dates. Some years, though, one may need to plant later, it just depends. Tomatoes really take off at this planting date.
I have never intentionally topped tomato plants either! I don't like to prune mine.
