For the MG, I suggest you use nerf or Spring Airsoft guns you don't mind cutting up. You can use wooden dowel rods as a skeleton and EVA foam as the "meat," and the wood would add a nice weight. I've not tried (as I don't have the resources, but definitely would love to), but it would be simple construction I would think. Try hitting Home Depot for little bobs and bits for the details. Done be afraid to get creative!