Stick with LST, autos can really suffer in the yield department if topped and/or chopped/HST.
This is due to the recovery time eating into the veg grow cycle, which can be as short as three weeks with some strains, by which time flower formation is initiated. So, if you only have a 3 week veg cycle, any technique that causes any type of setback, such as topping, whereby the recovery time is 7-10 days, this leaves very little time for veg growth. If this is your first time growing autos, stick with the basics and learn what is required to grow them properly, before setting yourself and your plants any challenges. 18/6 is best, from seed to harvest.
Whatever you do, do not try growing 24/0, your plants will hate you for torturing them with a totally unnatural sleep deprivation cycle of exhaustion!
Hopefully you will realise soon enough that real cannabis aficianados grow photoperiod plants and leave the autos to people who like "pretend" cannabis plants. Autos also require a ship load more electricity to grow and unless you have mega lights and have A Grade growing experience, don't expect any astounding yields. As you can tell, I am not a fan, having experimented with 30 odd plants over the last few years and with 35+ years of growing experience to back up my growing methods, I found many had totally unreliable genetics with many mutants and generally poor yields.
In the same time frame I would expect to harvest 5-50 times as much from photoperiod plants compared to what those autos yielded and have sworn off growing them ever again. Potency was also generally lacking, with only about 1 in 5 being anything exciting. They may have come a long way recently, but I just don't see the point in growing something that is going to flower, no matter what, when it is only inches tall. Have I put you off yet? I hope so!
Stick with photoperiod plants - much more stable genetics, better potency and yields to impress you and all while being less fussy to grow too. Look at the questions page on this forum, there are 99 questions about weird autos to 1 question about photoperiod plants. Does this not tell you something? It is hard to escape all the advertising hype surrounding autos at the moment, the seem to be the latest craze, but don't think you are missing out on anything special, it is hopefully a passing fad and will go the way of yo-yos soon enough.
There is no need to venture over to the "dark side", photos will always be better! Long live photoperiod plants!!
Sorry for the rant, just trying to warn you that autos are not special in any way and you are not missing out on anything by growing photoperiod plants. All autos are derived from photoperiod plants anyhow, so you can always find the same genetics, but they are more stable and with better potency because they don't suffer from the genetic hiccup that introducing auto genes bring.
I wish you luck on your new adventure, but yeah, LST is the way to go and definitely no topping for autos.
Hope this helps in some way,.........
Organoman. (and sworn enemy of autos!)