My main problem is who I want to cosplay FIRST haha. I'd say just pick one of your favorite shows and then from there decide who you see yourself cosplaying. It honestly doesn't matter if you look exactly like that person or even if they're a different gender. Just find someone you love and then decide if you'll be able to make/buy it!
I usually just wait until a character I like both personality wise and design wise shows up, adn then look into if I could actually make/afford it!!! That usually narrows it down to a reasonable number for me :) I don't cosplay anyone unless I love their character in every little way!