Welcome,

I suggest you look at the designs for the blacktoe 8x4, they have addressed many of the problems of the larger size, and its not as simple as scaling a 4x4 design. 2.5m long leadscrews are very big, heavy and have lots of inertia therefore other methods (rack and pinion, belt & chain drives) need to be considered. They also do a kit of the major parts if you dont feel like cutting them yourself.