Front mounting block, then a Front bag, S bag the smallest.
[front basket, being simple, probably lightest]
you put your pump/patch kit/tube spare in it.

easiest partial fold, roll is the 4 easy-wheel set for the rack.


bolt to mount the rollers is M6, so if you want skate wheels,
make sure the bearing ID is big enough

S bar is significantly lower than the M bar,
so better if a shorter [or]
younger for the bending over flexible person.

if light is your priority, the X version uses Titanium front and back parts,
and an aluminum seat post

start at a bit over $2K, though..