I will leave alone the question of what skill it takes to build a Legacy (noting only that you do need to be very careful and seek lots of advice.)  As far as flying one, though, the skill you need is the same skill you need to fly any airplane and it consists of an accurate and complete knowledge of what the flight envelope is and a conservative attitude that enables you to stay at all times well within it.  If your total flying experience is 35.1 hrs. in C-150s and you just got your ticket, I think you would be unsafe in a Legacy.  I also think that in far less time than it takes to build one, you could solve that problem.  Once you have that done, there is simply no reason EVER to fly a Legacy close to the edge of the envelope.

C-150s, 172s etc. were designed with the primary goal in mind of being idiot-proof.  Performance was a secondary (or non-existent) consideration.  Accordingly, you can do almost anything to them and recover easily.  Lancairs, and most other airplanes, try to balance performance against other characteristics, including recovery from unusual attitudes.  They also do not have the level of flight testing that is required of certified a/c and, as Brent observes, if you make it wrong, who knows what you have?  I have personally stalled the factory Legacy and, with Don Goetz aboard, we did approaches to stalls in mine as a part of initial testing.  Since then, I have not been within 20 kts of a stall except right after takeoff and flared for landing.  Unless you are a qualified test pilot, have extensive military combat training experience, have thousands of hours in Lancairs or are otherwise qualified to push airplanes right up to the edge of the envelope, don't even think about it.  You can do a very impressive show for folks on the ground without getting anywhere near stall.  I have done it the last two years at our local airshow.

It takes only a very little flying skill not to stall an airplane.  Anyone with at least that level of skill who stalls one anyway and crashes is not being killed by the airplane!