Up to 10 bulbs according to the instructions/box (with no hub).
This is true. Some Hue lights actually come with a Hue dimmer switch that is paired to work with the light out of the box. If you are buying the dimmer switch separately like this, you just have to pair it to your Hue bulb or light fixture. Although, as far as I'm aware, that means it can only control a single bulb/fixture, so loses the flexibility of the Hue system.
It will as long as the bulb is linked direct to the hue hub. I've got hue dimmers working with hue, osram and ikea smart bulbs and believe they will also work innr bulbs
These go on for £20 with the E27 light bulb. I wouldn't bother with this as it's only £17.99 anyway! Its £16.19p on Amazon
It does act as a normal switch with a hue bulb. Nothing else is needed- this dimmer and a hue bulb. The hub isnt needed with this.