There is a book by Vladimir Littauer (Commonsense Horsemanship) - he trained the US 3 day eventing team in the 1950s- who writes about "collection". He promoted forward
riding. A disciple of his Paul Cronin has written "Schooling & Riding
the Sport Horse" ISBN 0-8139 2287 9 $29.95. The answers to many of your queries will be found in those two books - and they are written by Americans.
I have reached much the same situation with my own mare but I query whether for my usages I should proceed with going "On the Bit" - although my mare will suddenly drop her head to the "ramener" position
and go "on the bit"' if asked to do so. She does it on a very mild french link bit with no tiedowns of any sort. It looks lovely -so I am told, but is it relevant for me, I wonder. The head & neck suddenly drop, the pressure of the reins lightens and the back of the horse rounds up. But it is tiring for the horse until the muscles have developed. Getting the horse down, is more about pushing the horse on from the rear, than pulling it down from the front.
For horses going down the road into higher and higher levels of dressage it seemingly is a must. For show jumpers it helps get the horse balanced back onto the hind quarters. For trail riding and hacking it is probably irrelevant - as Littauer writes.
But if you read the books then you can make up your own mind.
Reading also thru the various chapters of www.sustainabledressage.com
will help. As will looking up Wikipedia/"On the bit" - there is a good description there.
But this is one area where, in my opinion, you need a good instructor watching both you and the horse practising in the arena. A slight flaw in your seat will hinder and perhaps create problems down the line for the horse and maybe even you.
Please don't go the tiedown route - you'll perhaps wind up with a "false collection" - ie hollowbacked horse with nose pulled down.
Lord Loch gave me lessons years ago on his stallions. Nothing replaces being taught by a horse (as CS Lewis said). If you can find locally, a horse which will go "on the Bit" then convince somehow the owner to let you ride the animal. Training your horse to do it will take longer and first you must understand why and how. Allow that owner to ride your horse
in order to comment.
When you know all the answers then let me know.
Fascinating this hobby of horses -isnt it?
PS Some breeds of horse with short thick necks - ie cobs with draught horse blood find this movement difficult - whereas warmbloods ie Trakheners make it look easy. Presumably a long necked, long and low, well balanced, QH was born with an advantage.