Im trying to figure out if i need to take traits that have size increases to have models that are larger then 25-32mm.
I may not be reading the core rules pg9 about it right. by the way im reading it, it sounds like as long as the miniature needs a base of a certain size then its considered that size.
Ideally yes, but if you only had XLarge rules you most likely be good. If you were playing in a tournament or event the guidelines would most likely be followed to provide a standard. The goal is to have fun and huge model rules are worth getting to.
Here is an example: When creating a faction one playtester's model he wanted to use was a little larger than the rules for it when he created the faction. He just really needed to get one additional trait which could be taken later as he got a few games in. In the meantime the miniature was just that cool and no one even cared as he played the games using it.
The overlap in miniature sizes is there on purpose so as to not restrict gameplay based on the miniatures.
A huge miniature though ideally would be a huge model. Its a good guideline but really its most important that you and your opponent are on the same page when playing a game. Test it out have fun.