I guessed so, about the HSM i mean. Your choice seems very good to me. Will it be 1:1 driven or variable puleys

So how you plan to move the counterweight? I mean could it be better that the counterweight slides on a cheap round rail or something, for the sake of perfection? Inside or outside?
Inside would be better, cause it would not be seen and at the same time you have to make the beam bigger, so that means stronger, tough also means heavier.

I believe that for a proper build you should forget your worry about moving the thing. I have made various mistakes thinking like that in the past. You will make it perfect, it will make money, so who cares. Any way making something more than 120kg needs special planning when moving and possibly a machine to lift it. It would cost you exactly the same if you move 200kg or 350kg or 800kg, so concentrate on the final characteristics you need.