I usually like to get as much health as possible in kingdom hearts games soo how do you get the HP boosts in DDD?

you get Hp uprgrades in the ability link. depends on what spirit it is though http://kh13.com/forum/public/style_emoticons/default/ohmy.png

You get HP boosts through Abilty Links and by finishing the Secret Portals for the first time (you get a Hp boost for every Secret Portal except for the last one where you get Unbound Keyblade as a reward)

you get also a HP-Boost for beating Lord Kyroo

but I did this with Riku only and don't know if the bonus is also available for Sora