When i build stuff like this, i usually do a simple drawing first so i can come up with rough length estimations, then I'll do some calculations on loading. That way i can size stuff accordingly. I know that with the capstan winch I'm using I'll be right around 1k line pull, so i can use that for my calculations on stuff. Since it's designed the way it is (stiffleg derrick), the pipes are either in direct compression or tension, so it's easy to use a column loading chart for pipe columns to see what is an acceptable load (yes you need to do trig). I probably should scale it to see exactly what it weighs, but i think with my very conservative outrigger distance I'll be good. Basically you calculate your steel for the estimated loading, then I'll calculate overturning torque so the outrigger will have more. Once it's done I'll do some proof pics with it at capacity, so I'll know that I'm good within my wll.
I think the limiting factor will definitely be its tipping point, i made the mast tall enough to rig a few guylines if possible with the area to help keep it upright. The pipes are larger than needed, and will carry far more load than the rope will. If it's tipping while I'm dragging limbs to the machine, i could always boom down which would turn it more into a side pull rather than a tipping moment. Still thinking on the outriggers, i think i can still do one to the masthead for the side pull but the one coming back would need to be curved to fit around the tray better, which is still very doable but awkward. So I'm thinking one under the tray, and then one to the masthead out the side. The side one will be able to swing and stow away like the boom does on the other side of the upright post up front, so it won't take too long setting it up. There's a fair amount of rigging on this thing, but most of it should be able to be left alone and ready to go once i pull up.
I'm not really happy with the gooseneck, there's enough slop in the thrust bearing that it can get in a bind when the boom is more upright. Might not be an issue in service, so we'll see. So i might do something down the road to improve that, and if/ when i build another one I'll either get a better bearing or do one where the pipes touch on their sides like they did in the age of sail. The nice thing of building stuff like this is that it's only steel, so if it doesn't work like i want i can just cut it off and weld on new. Almost nothing ever works exactly right the first time you build something, there's always little things you didn't think of. So the drive to work on it until it's good is all that's required, not perfection right out of the gate. This will likely be a work in progress for awhile, but i think even in its imperfect form it still will run circles around me doing it by hand.