A 2m long version would be easier to fit the hardware into, but it would be significantly heavier in the water.
I would recommend for something this big to have no free flood ballast and rely entirely on pumped ballast. This would make it lighter to move to and from the pond than if you did it my way.
Also, this should allow you to lift something as intended. The water you would have to pump in to get the boat to waterline would represent the weight it should lift.
This is where I went wrong with mine.
If you can do it, I would suggest multiple pumped ballast tanks, say 2 or 3 down the centreline, and 2 or 3 down each side, this means a total of 6 or 8 tanks all needing individual pump controls to fill and empty. This can be done either with a pump for each tank, like mine, or, use solenoid valves to control where you pump to. Trouble is, I couldnt find any solenoids suitable! You may be luckier.
The reason I suggest multiple tanks is it will give you greater stability control over the model, especially when submerged. You will recall from my thread how sensitive mine is!