Hi Stephen, awesome news to hear
I think you've made the right choice purchasing an 18" f4.5 scope. If you're going 16" and have the cash, may as well go the 18" as it's probably the largest aperture scope that can be handled easily. The 20" is beastly territory
I too was going to hold off purchasing the ServoCat, but after speaking with many people and realised how much of a pain it can be to install after the scope is assembled, I thought bugger it and just cough up the dough. I don't know how people track planets at 500x+ mag, I can barely keep the scope in the fov at 400x!
The one big downfall to attaching the servocat which I found out later is that to separate the rocker box from the ground board is an extremely fiddly task, one that is not recommended by Peter as you risk damaging the scope, hence the whole bottom half must be carried as one piece unit in and out of the car
Perhaps you can get Peter to fit the argo encoders in so that you can attach the Argo unit at a later point?