you only have 1 mount for a thruster, so if you have a thruster mounted, you have to unmount it before you buy a new one

Rubber eagle is right, one mount for thrusters, keep the best one sell the others...that's all they're really good for...

As for the guns / turrets issue, there are also a limited number of slots available for each depending on what ship you choose to fly, generally with cargo ships they will have more turret mounts and fighters will have more of the traditional gun mounts (fighters usually have 1 turret mount).

Do you know how to mount/unmount items from your ship?

When your have your ship docked, go to the equipment dealer like your gunna buy some guns. Notice that on your guns that are equipped, there will be a blue box in the upper left of the weapon icon. If you click that icon, it will dismount the weapon. When a weapon is dismounted the icon "opens up" a bit like teeth. If you have a slot that an unmounted weapon can be mounted in, click the icon on the unmounted weapon and it will mount it.

To directly answer you question....no, the caviler does not have any turret mounts. Unless you think they are really great turrets and plan to change to ship that allows turrets pretty soon, just sell them.