I downloaded several new opts for my game. I installed them, they work and all, but every one of the zip files that have the OPTS in them, have just one opt. No cockpit or exterior, so it prevents me from seeing the actual ship. Is this normal?

Seems normal.

Bear in mind that most of the flyable TG fighters do themselves only have a single OPT file (which is used for AI craft & your external view) and use the same "general" cockpit.

So this example was followed by many people as there seemed little point in making an exterior which would hardly be seen and they could live with the "general" cockpit.
These days though thanks to the XWAU example the majority have started making all three OPTs for each fighter.