First of all, do not even consider topping your autos... that takes VERY precise timing to be successful and if you haven't grown that particular strain before, you don't know how long she has until she goes into pre-flower.... they COULD go into pre-flower within a week and that's not enough time for her to recover and therefore she won't be able to set her flowers... you'll basically have screwed your entire grow.
With autos, stick with LST or SCROG.. no topping, no mainlining, no major stress, period.
You can start LST at any time... just gently pull the plant over so the nodes are exposed to the full light or as exposed as you can get them.... keep them in place and let those new branches on the exposed nodes stay exposed to the full light... that's really all there is to it... you can keep LSTing them as needed....
Good luck!