I will have a 125 gallon tank or bigger by Christmas time for Link for sure. I've been watching videos of people's set ups and reading this site as well for DIY things. I just got a gorgeous stand with doors and drawers that will hold up to a 200 gallon tank - and I got it free, someone was throwing it out, I asked if I could have it and they said "get someone to move it for you and it's yours" so that's a good step and it's in perfect condition, not even a scratch on it!
The floor of the house will more than hold the stand and a tank full of water so no worries there. I priced out a Fluval that will work with either a 125 tank or up to a 200 gallon tank and that's on my "Christmas" list as well. I know it's double or more whatever the tank size is for proper filtration for a turtle, they can be dirty little things
I will say since Link was unceremoniously dropped at my door she has grown so I guess I'm doing something right. She has fresh quality water, a variety of food (she can be a piggy if I let her). We are going to the lake to get some river rocks (thanks for the idea Litefoot) and getting her some aquatic plants too (I read they also help keep water quality along with a food/play source for Link).
While at the lake we'll look for driftwood and ensure that it's cleaned outside very well before introducing it to the tank. We are also going to keep the 20 gallon tank as a tank for feeder fish for Link. Can I get those ghost shrimp for a feeder tank too or do they not mix well with fish?
I'll be adding Link to my Will as well, I just have to find someone who I can leave her to as my son is not even remotely interested.