Are they fine? I heard that I should try to keep it simple, but I don't see how I could fix it this time. Anyway, do they really start to lag? Because so far my model has 14 of those, and it's bothering me how high that number feels.

sometimes you can't avoid it, however you should try to keep them in quads to keep your mesh clean, this helps with animating. If the object is a static object, it likely wont affect it as much, but chances are if your over 5 points you can opitmize it into quads, even triangles would be better in terms of a clean mesh, end gons are the devil >..>

Models are turned into triangles upon export/import anyways, as that is what all modern graphic hardware is designed for. I'm not sure what you mean by "5 parts" though. Generally, for ease of modelling and animation you should be using all quads which would be four vertexes.

Unless you're referring to something entirely different?

Hard-edge objects and non-bending/flexing objects won't matter as much, all-quads lends well to good edgeloops and topology.

However, no matter the model type, if you leave a lot of n-gons, you lose control over how the triangle mesh gets "mapped" which can result in some weird texture mapping and shadows.