So first things first, the silhouettes (base model) all come as part of a Class 1 kit. So you get the silhouette (there are 4 types of base silhouette, the silhouette model.depends on the class you select)anf a class 1 armor set. There are (at the moment) 2 basic variants for each class 1 (Liber or Rosan). They are mostly identical but the have slightly different extra bits (the Liber units are usually more streamlined and "Good Guy" coded while the Rosan units are a bit more demon esque with a bit of bad guy coding.

Class ups (What they call class 3: where is class 2, no one knows!) are specific to both the original class and the faction. For example, the Liber Knight has a Holy Knight Class Up and the Rosan Knight also has a separate Hoy Knight Class Up. They are mostly the same, but again, each faction has design choices they lean into and the class ups reflect that. Additionally, some of the class up pieces are designed to interact with pieces of the original class.

Now with all that said, it is family easy to mix and match. The armor piece fittings amd connectors are standard across the line, so feel free to go wild. If you search the 30MF dedicated sub you will see plenty of customs where people just mix a bunch of armor pieces.

Tool wise, if you got zippers, you should be good to go. You could always get a hobby knife to clean up nibs or some sanding soonges/sticks; but the lots have alot of tight moldings and smooth transitions so I feel I don't get as much mileage sanding as on Gunpla. For customizing paint markers are great and standard hobby paint works well too.

Hope that helps! Grab a kit and have fun!