a word of warning
my personal recomend isc 300/350 rpm , at the paddle wheels, and i use either 1 or two motors of 540 size , about 42mm diam, these motors seem too small to me ?especially w the size of the model
I normally drive a paddle wheel in 1/24 scale, about 170/190mm in diam., via tooth belts 3:1 reduction, so 1000 rpm motors and g/boxes via ebay
but another fellow has used 150 rpm jaycar motors/g/box , and over driven them to get enough revs,1:2 ratio
you need the top of the floats about 6 mm below the water line to allow for water scoop
i use HTD belts in preference to MXL, i have stipped MXL by not turning on the TX first , and brass paddle wheels, have a fly wheel effect , taking 3 teeth off each belt
if you get into trouble , try these ideas, but you may be ok
good luck

there are a few paddle models at goldsmith steam rally, every time