I've tried 1 & 2 above.
My problem has always been getting good depth of field. About the only
way to get everything sharp in, say, a rosetted drosera is the boring
top-down shot with the lens axis perpendicular to the plane of the
rosette.
Bright light helps a lot since you can use a high f-stop, but it is
still a hassle since the lens usually shades the subject.
I've been toying with the idea of buying a "ring" flash for taking plant
photos. This is a circular flash unit that mounts like a filter on the
end of your lens. The high intensity light permits a really high f-stop
(like 32 or 64) and the ring setup ensures an even illumination.
Another item I'd really like to get is an enhancement of #4 in Barry's
list: A bellows system. Unlike a fixed extension tube, a bellows is
continuously adjustable so that you can get any magnification you want.
-- Rick