There is "Legally" qualified, and there is "Really" qualified. I agree with those who say that the minimum "Legal" qualifications is a PPL. As to whether or not you have the skill and experience qualifications, well, there is quite a bit of documentation available from the EAA, and a lot of personal help that can be given by EAA Flight Advisors.
Lots can go wrong on first (second, third, fourth...) flights. Surprisingly, most of the things that can go wrong are actually trivial - in hindsight. Aside from basic stick and rudder skills, and experience with checking out in different airplanes, I like to ask people "what kind of emergencies have you dealt with in flight, and how did you react to them?" Over-reacting to an emergency can be as bad (or worse) than under-reacting, or reacting incorrectly.
What do you do when your oil pressure gage goes funny? Or your oil temperature? Or, on that initial take-off, your tach value isn't correct? Abort? Go? think about it....oops! You're out of runway! All of these things could be simple instrumentation, not a real problem - it would be a shame to ruin a great new airplane because you reacted incorrectly.
Let's not be to high and mighty about this - flight testing an RV built to plans with a Lycoming engine is NOT "Experimental Flight Test" - more like "Production Flight test". But....you can get in trouble very quickly if one of th many, many common "funnies" occurs and you don't know how to react to it.
Have you flown an airplane that is drastically out of trim before/ Or has a stability issue? The questions keep coming, and these questions (and your personal answers to them) will eventually help pilots realize if they feel good about your first flight or not. Are you excited in a good way? or dry-mouthed with a bit of worry.....
As I said - there is "Legal" - and there is "Qualified".....I advise everyone - even those pilots with thousands of hours - to talk it over with another experienced pilot before committing to a first flight. Sometimes, we all need an outside, dispassionate opinion to help us see the big picture.
Paul