I often take the bottom node off regardless as it seems to never grow as thick and well as the nodes above it.
If you’re set on doing a mainline.. go for it. But it’s a risky proposition on auto.
I would recommend just topping when you want and then let the branches grow out, once they’ve got some length, tie them down. But more than one topping on an auto can seriously throw off your yield and quality.
If you just are wanting to experiment and don’t care about how the end product is.. more power to ya! Try it out. But if you want decent results I wouldn’t go beyond a single topping.