If you live in a relatively flat location a 3 speed or even a 2 speed brompton will work fine on a small wheel bike. i own several bromptons a 3 speed[sram t3] a 5 speed sprinter hub and a 6 speed[sram t3 w/ 2 cogs] and a Raleigh Twenty with 2 speed duomatic and another Raleigh twenty setup as a single speed. the 5 speed i have has the old english sturmey 5 speed sprinter hub not the new chinese made SA SRF5 hub. the 5 Sprinter has the same low/high ratio as a 3 speed hub the 2 extra gears are in betweens. the 6 speed has extra low and high gears which i don't have much use and the shifter just adds complexity to shifting. the gear pulleys mechanism must be kept clean all the time otherwise you'll have shifting problems very prone to dirt contamination as its low on the ground.

as you bike daily you build leg muscle strenght and eventually won't have a need for too many speeds. my favorite bike i use is my raleigh twenty duomatic only 2 speeds high and low. If there's a sizeable grade or uphill i just stand on the pedals and I make it to the top fine. If theres a hill 1 mile long let say I just don't go tackle it and go around it its not never fun going up unless you love a real work out then you don't need gears. I don't.

my 2nd favorite is my Raleigh single speed very light and simple nothing needs to be adjusted and I just do fine on hills as well as its geared low for just cruisin.

if you keep shifting gears each time theres a little grade then you will never build leg musles. once you build them you will find you don't need gears after all not bragging but I don't

I believe in less gears less trouble !