I am want to install Brazilian Cherry.
1------Is this going to be so hard that it is uncomfortable to walk on?
2------My wife is a floor scratcher. I love her and I accept this.
So, will this resist scratching?
I need to keeps costs seriously down because I have to do a lot of cosmetics in the house.
3------I was thinking of just putting the unfinished floor down, giving a quick vibrating sand and then applying an oil treatment like teak oil or Danish oil.
I have a local guy to put down the wood for $1 a foot and I can do the oil and sand myself. Maybe I can get the installer to do install and sand for $1.5 a foot.

4. ----------are there any special considerations for this wood? Does it expand more?

Anyone?

Canofworms. Yep that explains it well.

1- No, absolutely not.
2- Resist? More like depth of scratching, dings and dents will be shallower compared to other hardwoods.
3- Not going to be that simple, unless you can live with an imperfect floor, or one that looks like a rushed weekend project. Over and under wood is going to be an issue if what it seems you're looking at price alone in this project. IE buck a square foot to install..real cheap...makes me wonder what kind of product you're looking at. Expect problems with a cabin or lower grade or whatever they want to call it.

Teak, Danish oil. I've never heard it used on Brazilian cherry, but I'm not a finishing guy.

4- Changes color radically. Quite dense, but like all hardwoods, it needs proper acclimation and attention to floor preparation for any chance of a successful installation job.