Will this addon affect my performance?

SAM FollowMe has literally no impact on your fps because it's only active when you started the guidance to your parking position and even then only one vehicle + route is being calculated. If you compare that to a flying aircraft...

Do I need a specific airport configuration/setup?

Not as long as the airport uses a correct AI taxiway network which 99% of all sceneries have. We're using exactly the same route network like the AI traffic does so that should work out in most cases. It also doesn't matter if it's a default or custom scenery.

Are the vehicles animated?

Yes, they use wheel and steering animation as dynamic head- and taillights and custom light and sign animation depending on the vehicle type.

Is there a 3D marshaller on every parking position?

Yes there is. You might already know our marshaller from other SAM compatible sceneries. This friendly guy will be placed automatically for any parking spot, no matter of the airport/scenery. It will also take any custom scenery using SAM into account so no doubled marshaller as well as VDGS driven parking positions will appear.

Why is the vehicle not following taxiway markings properly?

The vehicle will drive along the AI taxiway network which is not related to the visual lines/markings that you see in X-Plane. Depending on the setup of the scenery there might be offsets or steep turns which are not 100% in line with the visual appearance of your scenery. We propose to contact the scenery author in that case or for gateway airports fix it yourself by editing the network in WED.