Hi,
according to my experience (the last time with model Lulonga River steamboat) I would recommend a geared motors with the maximum speed of around 150 rpm for Graupner paddle wheels Ø 140 mm.
I use a simple external V Tail mixer - throttle for speed, and mix ailerons for ESC.
I can so with a single stick to control both speed and direction. The rudder for my Lulonga model is inapplicable , as to classical the steamer ,the rudder will surely have better efficacy.
On my first live steamer Ned Kelly(australian type, wheels mounted on a common fixed axis), I had only controlled the rudder, the model was quite handy;rudder but was somewhat larger.On a boating exam, I used substitute wheel from plywood (graupner wheels I got up later).The model was 115 cm long (o.a)

Wishing success
Tom

We used to have such a model in our club and having worked on repairs for the owner I recall that his model had a couple of 500 size low rev high tork motors driving the wheels via a cog and chain system. The paddles do not need to rotate very fast (