LMP
You have recieved some great advice here.
Spend some time talking to other longbowers and gain as much knowledge as you can.
Join the British Longbow Society,its only six quid a year, for more info.
As Will Selfbow said don't get drawn into the poundage bit get a bow that feels right for you.
A friend of mine shoots a 20lb bow with 1/4inch shafts and she usually comes first at the NFAS field shoots we inhabit.
Shooting a longbow well requires determination, practice,time spent matching arrows but the joy of getting it right is just reward.
I wish you well in your endeavours,and as someone else pointed out somewhere there is a lot more archery out there besides
GNAS.