500 for sure
also we just recreational sail my 450 with 2 adults all the time
once we had 3 on it..you get very wet but have alot of fun
when we had 3 on it we stood her up on her nose couple of times but she bob's up and out like a cork..the sails fill and off we go again..2 or 3 on a 450 is not advisable..the 500 will fit you better.
also you can add all the options you want to a boat but it's pretty tough to add a couple of feet.
you can also sail with just the main if you want when you're solo
Carl