Can I use Time Capsule as shared disk

Just to add to the first answer, yes you can use it as a shared drive (I do) It will also work with PC's not just Macs, so for example if someone came round your house with a Dell laptop you could give them access to it.

This is a great way to share photos with friends, and also a good way to back up a PC as you will not be able to use Time Machine.

To answer the hardware issue, you will not need any additional hardware providing your computers have WiFi cards if not then you will need a WiFi adapter, or you could connect via ETHERNET.

Yes you can. When you have the time Capsule connected to your home/office network, all other Mac's should be able to see that Time Capsule and with the right password should be able to access the data.

You can also use it as a Time Machine backup drive for various Mac's on the same network.