Templates are pretty much the domain of the GM, ask them which are 'available.'
Template stacking isn't really confusing as long as you do each template one at a time, apply the changes and verify the creature is still a valid subject for the next template. Basically it makes a difference which order they are applied.
Well, we know how to, it's just a debate about what characters can and can't be stacked with.
Basically multiple Half-templates doesn't make sense, as there wouldn't be any of the original creature in the mix.
Half-fiend, Half-Red-Dragon T-rex. a small lake of alcohol may or may not have been involved
...a small lake of alcohol...
A Drunken Master's greatest Wet Martini Dream. And a hilarious image.
What about half dragon half vampire, half lycanthrop vampire, half fiend vampire, half celestial vampire, half fiend lycanthrop, etc? It doesn't make sense... Clearly you can add the animal lore template to any template and the worm that walks template to any spell caster with any template... but certain templates don't make sense stacking together because it says you have to be humanoid. It doesn't make sense because if you are a humanoid creature and add a lycanthrop template or a half fiend template etc, then your sub type changes to an outsider or outsider native. Once you're an outsider, you are no longer considered a humanoid.
As long as the template is 'legal' at the time it was applied it doesn't matter what it later turns into via another template, RAW. That is why I said the order of application matters when applying stacking templates.