Hey i think thats good for your first time with a 400w! Works out at 0.77g/watt, alot of posts i have read state that alot of people aim for 1g/watt but dont often acheive it.
Training will generally increase your yeild to an extent that it does pay off.
Id say fimming/topping your talking add 2-4 weeks extra for decent results.
LST couple of weeks at most extra, may not increase your time but just create a more even canopy.
The general principle is that lumens diminish quite significantly over a short distance using indoor lights, therefore the closer the bud is to the light within reason and not taking into account heat the larger the cola.
So you want as many colas as possible to be as close to the light as possible hence training.
I see an xmas tree shaped plant indoors as in efficient assumin that it is xmas tree shaped and the light is above.
However everybody has their own views, find whats best for you.
Mines recently have had about 6 weeks veg been fimmed and lst'd and then put under a scrog net.
That helps me position buds, keep the canopy evenish and when the buds do finally chunk up they have support which should increase the bud size and stop them falling over.
This crop ill be happy if i get 1g/watt in coco done on budget.
Next crop in rdwc with a larger budget id be aiming for atleast 1.5/watt.
There is alot to it my recommendation to you would be to take it one step at a time, youve done awesome for your first grow. As a beginner i would set my expectations at the 0.5-0.75g/watt mark a grow anything extra is a bonus.
Expirement with lst and if you are really struggling to get those side branches up fim.
In essence training can be very efficient and certainly worth while but one step at a time youve done good.