Quote: "Would MP10 fit in?"
At the risk of shameless self-promotion... Yes!
Seriously though. If you only have money for one pack
now, get MP3 and get MP10 later when you're further in development. It's a lot easier to switch out weapons than to recreate levels.
At the risk of further shameless self-promotion... With Mps 9-10, You get a lot of options for weapons when you factor in new and upcomming weapons on Game Creator Store which have the same hands. I estimate there will be close to another 20 weapons before that hand mesh is retired. Overused or not, I think it's largely perceptual considering that sure, they pop up in a lot of WIPs but I believe there's only a few completed games that use them.