Very good advice to judge when to begin flowering, by observing how much space is left in your grow area.
Most of the time Clones are vegged froma minimum 2 weeks all the way to a full 8 weeks.
As far as nutrients; All you need to remember is that it is not necessary to feed nutrients to the plant until there is an established root zone.
I would advise you to use a 20/4 light photperiod for clones. All plants need some rest. This will also allow some minimal stretching to occur during veg, so that it all does go leggy on you, when you induce flowering 12/12.
Good Luck. More info from you as far as strain, etc…would allow us to give you a more educated response. Peace