I tend to be heavily focused on DIY and buying used equipment so I may be biased, but If I were in your shoes I would consider two things-
1) When you get into specialized complex designs like this, and you buy commercial, you're locked in to what the vendor came up with. If you design a riparium or paludarium from scratch, you can get the exact layout you want.
2) Resale. These things are an incredibly small market. If you ever want to change your mind, will you stand a chance of getting your money back out of it?
Also, the $1300 price you quoted for JUST THE TANK makes me want to puke! Grab a used 75 or whatever from Craigslist, spend some quality DIY time, buy the lighting and filtration used (the one you're looking at is used anyways, right?) and I bet you can come out at a fraction of the $750 they're asking...