fietsbob

not Sammy, but,

For Q#2, It's a half meter, 50cm, [saddle clip bolt to bars is 650mm]

I fit the EZ wheels .. they're thinner than rollerblade wheels
and less heel strike than with the original wheel.
same sealed bearing in them, as skate wheels.

Extended post + a SAP for a bit more setback than the Pentaclip or standard type saddle clip allows.

Of course with telescopic combinition, substitute a different
integrated saddle clip /seat post for the upper section,

and maybe that will be sufficient for you,

I was able to fit a Fizik Vitesse CP3 on with the saddle clip spun around,
and its just the right cush for my tush, nicer than the one Brompton sold.

Still have the swiping of QR seatposts to contend with, if left locked on the street,
in places that shun you bringing it in ..