It seems to me that docking a proa has some things in common with other
multihulls and some things different. In common is the fact that because
of the light weight the windward end is going to blow off quickly,
making monohull-style slow approach and angle judging less applicable.

Different to other multis is the axis of symmetry. What I mean by this
is that the main problem when docking a normal multi is that the head
blows off. The cure is to turn the boat round and dock in reverse. This
works because it doesn't matter which side you put to the dock. But on a
proa there is a preferred dock side, though clever design can minimise
the issue.

Given that background, the following thoughts occur to me:

(1) As with any multi, having a steerable main motor is highly desirable
for slow-speed manouevering.

(2) Some means of stopping the windward end blowing off is essential. I
can think of four possibilities:

(2a) Move the main motor from one end of the boat to the other. This
assumes that the motor is mounted towards an end rather than in the
middle, and it assumes some kind of transport. Probably impractical!

(2b) Add drag to the downwind end so the stable attitude is the one we
want. The most obvious way would be to let out some jib and sheet it
appropriately, or perhaps add a temporary 'mizzen' at one end. With
careful design, I think the extra drag could be balanced by the
steerable main motor.

(2c) Apply a counter-torque using an additional motor a la catamaran.
This is what you're already planning and I don't see why it shouldn't
work. Given you know the separation between the motors and Rob has some
idea of the windage, it ought to be possible to work out the maximum
wind speed before there starts to be a problem.

(2d) Apply a counter-torque using a cross-thrust trolling motor mounted
near a bow (bow thruster holes probably aren't acceptable IMHO). Looking
at the diagrams of Visionarry, it seems you won't have a lot more
leverage in this position than the second main motor does. Perhaps
double at best. So a 'bow thruster' seems likely to be too much weight
in the wrong place if it's to give you more counter-torque as a second
main motor.

So my SWAG is to rely on the two main motors and in extremis either dock
with the wrong side to the dock or let out some sail.

Cheers, Dave