You cannot do solid site finished hardwood on concrete slab. The foundation type determines your wood choice. You must use engineered. Which can be glued down any way you want. Solid hardwood is nailed down perpendicular to the joist.

It is a condo and lots of people have hardwood, glued. There are no joists.

That would be engineered wood, glued. Not solid. Engineered is real wood too.

All engineered is pre-finished and I want to be able to sand in the future.

Engineered with enough of a wear layer can be refinished a few times.

You can do a nail down hardwood floor if you lay 3/4" plywood subfloor over a vapor barrier over the concrete. This will raise the floor level up and could create problems with transitions to other room floor finishes. You should consider humidity and other moisture factors with this installation.

You can turn the flooring pattern with suitable transitions between rooms or areas. You don't have to run it all in the same direction.

Good Luck with your project.