Hi
If I'm looking for low poly models, I try to use models with much less than 50k poly. Usually I allow characters to have 10k to 20k polys and any other 3D-model in the game less, according to it's importance/visibility in the game. If you try to target mobile low poly market (or probably also VR), then you should go even lower in polycount. As a general rule just try to make it look best with the least amount of polygons and work a lot with good texturing. As for materials / textures, I try to have simple materials and therefore only use a diffuse texture unless there is a very good reason to use an additional material.
So to answer your question if a 10k poly weapon is ok:
- For a computer / console single player game, e.g. an RPG, FPS or fighting game - sure
- In a computer / console real-time strategy game and every unit will be carrying it - no
- In an MMORPG - probably also rather no
- Mobile device - no
- VR - not sure, I don't have enough experience in that field yet, but I would go for the lesser the better.
So that's what I would recommend, I hope that helps :)