Looking at the photos I would say that yes, the wall needs painting.
Might I suggest the calming and non - offensive tones of Magnolia as an option?
To the boat: The pipe you have looks to be a water cooled Prestwich pipe, I may be mistaken but am fairly sure it is. If it the size I am estimating it would indicate it is for a 10cc motor. About.
The drive on these boats I am not sure of, the hardware you have looks kind of like what you would use on surface drive, but the strut you have looks like it is placing the prop too high on the transom on your boat to achieve surface drive.
Can you adjust it up?
Engine mounts: You have basically two choices:
1; fit "rails" - 1/4" ply running fore and aft at 5" centres which the engine mounts are bolted in between.
2; bond fixings into the hull that the rubber mounts fix to.
Choice is yours, both systems have advantages and disadvantages.
Looks like you need the following to complete:
radio box, engine and mounts, prop shaft tube, prop shaft flexi, prop drive dog, water pick up (unless the rudder has one built in), a fuel tank.
Just noticed that you are planning a .90 in it. Might be a bit too much engine, will be interested to hear other members input.
I have never seen one of these running in the flesh, will be interesting to see this one get up and going.
Good luck. Have fun.
Glenn