You wouldn’t need that many 10Gb devices. Just one(s) that split up the traffic to other devices. Either the ISP router needs to split it up or the device that does the splitting should be 10Gb. If you go with 2.5Gb youll be losing 0.5Gb, assuming you actually get 3Gb from your ISP.
The intent isn’t to get 10Gb to every device, but to actually be able to use the full 3Gb you’re paying for. Right now it looks like you’re wasting 2Gb of your bandwidth because everything goes through your personal router which is limited to 1Gb.
By not having one. I just use Pandora.