Back to the Perry plastics, besides the European Mercenaries boxed set, I would recommend getting at least one Light Cavalry 1450-1500 plastic boxed set. This provides you with 12 cavalrymen that you could kit out e.g. as mounted Swiss crossbowmen or Swiss/allied cavalry with spears. Furthermore, it comes with a wealth of plastic bits, such as new heads (including a couple of distinctly Swiss looking ones) that you can add to your plastic infantry for some variety. Due to these extra bits it is a good idea to get a boxed set early on, and not only once you have built up all your infantrymen...
As for the other plastic kits, also the Foot Knights 1450-1500 might provide some handy figures for captains to lead your units. The whole set (of 38 figures) is a bit excessive, but if you can easily get a single sprue of 6 figures from somewhere, it might be worth it. Failing that, there is a wealth of dismounted men-at-arms in metal available from both Perrys (in the Wars of the Roses range) and Steel Fist Miniatures.