Re: "Teaching" how to jump
There isn't necessarily a formula in how much or how fast to go, but I would rather err on the side of going too slow. Your horse will often 'tell' you when he's ready to move on. I keep the fences low until they are a little bored with it and there's no sign of anxiety (over jumping, rushing, etc). In fact, I usually keep the fences low until they're jumping lines and even courses before I start making them higher.
At a show the lines will generally be set off a 12 foot stride. So yes, 6 ft before and 6ft after the fence for take off and landing. Lots of horses won't necessarily be a 12 foot stride though. On a greener horse with a smaller stride I will often set it off 11 ft (still keep the 6th landing and take off though) just so it'll be easier for them. I will set out poles off a 12 foot stride to work on the correct forward pace though just to get them stretching out enough and then work the fences in when they're comfortable with their new pace.
I personally think the 3 stride line is the hardest! In a 2 stride there isn't as much room to get in trouble, and in a 4 stride there's enough room to get out of trouble. 3 is just in between. When I first teach a line I like plenty of room (like 5 or 6 strides) just so the horse has a chance to regroup and prepare for the next fence.
There are a LOT of training strageties out there, these are just some of my personal thoughts! Good luck!