30 watts should be good enough for most things you will encounter. don't go crazy though cause if you get one too big, you chance frying the traces off the board with heat.
as for tips, i usually get what i can only describe as a cross between a pointed and chisel tip... it offers a flat area that can be butted against leads while having the flat portion against the trace itself. then when rotated 90 degrees it has a narrow profile for small leads without touching anything else.
but some people prefer the cone shaped ends...but if you purchase a kit that has a few different kinds of tips, you will probably find a particular shape that will work good for you.