This sounds like a cool/fun display project. It would be more appreciated and better critiqued with some pics though.

200gal is huge for a BP. But if it's gonna be a landscaping project like you want it to be and you have a ton of coverage(large leaves and the like for him to hide under), I don't see a problem with it.

I'd be weary of the chipped marble as well and get the coolside temp closer to the 78-82 range.