I want to top my plants but am new to training. Ho...

https://www.cocoforcannabis.com/topping-cannabis-plants-why-when-how/ This should give you some answers. Personally, I top depending on a mix of node number and height, usually around node 5. - Since it's your fiirst time, you should expect it to stop growing for a week or so.. It might be faster if you get lucky and do a good job at it, but statistically you won't so don't worry too much if it halts growth for a while.. It'll start growing again once it's healed up. Good luck with your first topping. ^_^