1. Yes but I would change the words.
"If so, you might simply want to try to buy over the domain name from the current owner."
To use could, I would change it to, "If so, you could simply try to buy over the domain name from the current owner." You wouldn't need want there!
2. Simply means something more like "only".
3. I would say "buy" instead of "buy over". I get what you mean though :)
Hope I helped!