Hey m8...
Looks like you are off to a great start..and have already been given some good advice...

The stretch you will get is due to a couple factors..one is heat..the other is amount of light...
If you keep things cool enough the plants will not stretch..in that case the plants attempt to space out to allow air flow between the branches..
And if you give em lots of light they will remain a fair size...mine were flipped to 12/12 at about 10 inches..and they are now in wk 6 of flower and have not quite doubled in height..but they are heavy with bud and as you can see there is no stretching..that's because I keep em in a space about 2ft by 4ft..and give em 600 watts of HPS light!
As you can see I am also a user of Advance nutes..or rather..I selectively invest my money with them..
I use their flower enhancers (bud blood..big bud powder..liquid overdrive) but I use cheaper stuff for my base nutes because I am happy with the results I get..
I have a post in the advanced section here outlining products that I use..from start to finish..have a look and if you wanna try it I guarantee you will get better results than if you just buy a couple bottles of this and that..
It's not just about what you give em..but also when..
I have been growing Serious seeds Chronic and White Russian and have to say I am OVERJOYED with the WR...
The Chronic has been good..but not as good as the WR so I am going to grow JUST WR next time around in my home garden (I have 3 gardens I have franchised out to new gardeners..I give them materials..plants..and advice and they give me 1/3rd of each crop and we split the honey oil and baked goods produced with the stuff that isn't suitable for smoking)..
Remember this m8..if you go cheap you will lose on the scale at the end..so think of it as an investment..the more you invest the better your results will be...
Johnny
P.S. The first 2 shots are my moms..the next 2 are my nutes and temp and humidity level..and the rest are my crop..