A “highway” is usually known as an “autoroute”. “Sortie” is the correct term, and “Entrance” is “accès”, but it is rare to see it in use outside technical stuff. “Highway ramps” are known as “bretelles” (either “bretelle d’accès” or “bretelle de sortie”).

To add in a related term, an “interchange” is known as an “échangeur”.

Is “sortie” correct for referring to an exit from a highway, and is
“entree” correct for the entrance?

Sortie and entrée are both correct. accès may be used instead of entrée.

Also, how would you say the “exit ramp” or “entrance ramp”? La rampe
de sortie et la rampe d’entree?

Rampe de sortie is correct, rampe d’accès might be used (instead of rampe d’entrée). Technical terms are voie d’insertion (or voie d’accélération) and voie de décélération.

Lastly, is “grande route” the correct term for highways?

An “highway” may be translated as autoroute and sometime as voie express.

The French traffic code refers to both as route à chaussée séparée (divided highway) and to route pour automobile (casually autoroute) and voie rapide ou voie express (casually voie express). Difference between autoroute and voie express
are technical and safety level.

Urban highway are usually know as rocade or périphérique (the former only apply for ring road).