When To Top

I was wondering since i'm mainly an outdoor grower,when should i top my plants so i can get them to bush out more?Also how many times should they be topped by the time the reach 3 foot high,I have them in 5 gal buckets so i'm not worried about them not having enough planter size & i have a tall closet so i can let them grow as much as my light will let them which is a 400 watt hortilux light.There about 5 inches high now & i still haven't feed them any plant food yet,so i'm looking for alittle info on when to feed and when to top so i won't screw it up since there looking so good lol!Thx for any info!

Height in inches is not as meaningful as height in nodes. Top after the 5th node and then again when the side growth has 4-5 nodes on it.
You should not start in a large pot. Start in a SMALL pot and re-pot frequently. FYI for next time. The plant will still finish rootbound very often even if the pot is large, if it was put in a large pot too young.
You should plan to flower at about 18" high instead of 3 feet because the plants will double in height during flower, adn a 400HPS does not have all that great canopy penetration.

Thx for the in , i never thought of it that way,this only makes my 3 grow in side and it has been so long since my last one i forgot most i had learned from my mistakes lol.I'll let them get about 18 -2 foot then i,ll put them into veggie mode & see how the do,i know that the Big Budda chesse can make some huge buds from my summer grow,and it was worry free the whole summer.I'm also thinking about buying me a 600 watt light anyway i wish i had when i bought this one.Thx Again.