Ummm... I don=B4t want to be a critic here but beware of generalities.
First of all, boat size depends one what you want to do. Personally, I
wouldn=B4t be caught dead in some oceans on a vessel less than 34 feet.
I know my limitations and I like stability. I want a heavy keel under
me if the s&%* hits the fan. But I know many people (friends, not
acquaintences) who are happy on 30. Go sail a few boats in heavy seas
first. Then decide.

Engine depends on vessel design, not just LOA and displacment. Check
the designer=B4s recommendations, then decide how much fuel you want to
carry. If I had the space to carry the fuel, I=B4d go for the bigger
engine in the designer=B4s specifications only because I sail in seas
where I might need that extra power...

Construction material is another world unto its own. I like metal. But
I own metal. I=B4ve sailed fiberglass. It=B4s bloody strong when
constructed properly. I prefer not to take it into ice, but some people
down here have. It=B4s plastic, of course it can be watertight if
constructed properly. Watertight bulkheads can be a good idea. And NOT
all fiberglass is cheap. Ever look at an Oyster?? The key to fiberglass
is that it=B4s compartively easy to maintain and more difficult to
=B4melt=B4 with another metal. Ever see what copper does to Aluminium?
You don=B4t want to sit in a poorly grounded marina with an aluminum
boat. It won=B4t be there if you leave it for a couple of weeks.

There are lots of good boats out there that vary in size, material,
layout, etc... Know what you want to do first.... then look at what
boats sail in those conditions...