I think the general consensus is that something as big as an F18 or N20 is probably not a "first choice" for you if your primary sailing will be single-handing. Unless of course you:

are really buff
Preferably over 220.
Have two pairs of hands for all the control lines, tiller, etc.
Only sail in flat water with steady wind under 15 kts.
push boat around on hard surfaces and not up steep hills/ramps