The answer is yes and no, some are tight others aren't so much so.
The chairs do come off the sleeper, they are on a spigot, I have used an old 3ft length of Aristocraft removed the screws and sleepers and then threaded them on.
As I say some of the chairs are a tight fit, over the rail ends, and indeed over the underside sleeper fixing screw holes as well, (Note for the future, smooth off the underside screw holes.)
As for spacing just used the old chair witness marks and lined them up that way.
With 11 sleepers per foot you would get just 5 sleepers short of 5 ft per pack, visually I think you could get away with 10 sleepers per foot, give you the full 5Ft per pack.
Over the last few days the 3Ft length has been chucked around the house, connected to Piko, LGB and Aristo track, and generally used and abused as they say, only have to straighten a few back up, but its only one side per sleeper that slips. One thing of note, they have a short and long outside side, visually is only a few mm, but it does stand out, easily solved by turning the sleeper and re fitting to the chairs, if you are into perfection.
BTW aint run anything over them yet...
I need to get round to doing a proper review, but other matters are pressing here ATM....