The sky is not the limit. lol I know it is going to be a hefty build, but I also hate wasting money. I know you can spend as much as you like on anything. I have a number in my head that I'd like to stay under - but that's including room modifications, cabinets, plumbing, electrical (I think I'll need to get a new fuse added to the fuse box, but I already needed as part of the house control system), etc.
The CO2 and CO in the garage is an interesting point as well. I'll have to think about how to get around that. I have been thinking about the climate control of the water and battery backups in case of power failures. There's systems where you can tell it to keep everything online up to 90% battery life then start cutting things as the battery is dieing. The last thing to be cut, I imagine, would be the climate control stuff. I have a system like this in my house, and the last thing to cut in case of power failure is wifi and security system. The tv's and sound will stay operational for about 2 minutes. Which is nice if it's just a quick flicker.
If I were to get some of those species, I would definitely plan around them. I don't think they're in the immediate future though. Maybe a few years down the road.
The house does not have a basement but it does have a decent sized crawl space. That was one thing that surprised me when I moved to the area. Very few homes have basements. Apparently the ground is too hard or something. I'm not sure what you mean about plumbing to the kitchen. I will have to look into that to get an idea about what you are referencing. I already check the tank on breaks! And make breaks to check on it, and it's not in my office! LOL That's why I will only keep a small desk in the room, and move my main office to another room. Plus, I'll have more space for the tank(s) that way!
Several homes in the mountains here in NC have basements.