Yes, S130 allows up to (correct me if i am wrong) 8 connections as central and 1 connection as peripheral. Newest version of SD may allow more, but i am not sure because of no documentation released yet.
Yes, the nrf51822 will work as a central/observer role and act like a AP. You can flash it with S120 or S130 and try the ble_central example in the SDK 8/9/10. It can connect to up to 8 peripherals simultaneously.
I'm not quite sure if I understand what you mean, but:
The nRF5s supports Bluetooth Low Energy (aka BLE or Bluetooth Smart or Bluetooth 4.x), ANT and proprietary protocols. None of our chips supports Classic Bluetooth (BR/EDR).
If you are talking about connecting two or more nRF5s together in a network then I suggest that you read up on Nordic's Softdevices. These are Nordic's own proprietary BLE protocols, specifically designed for the nRF5 series. As @Wojtek and @ldmxhj points out the various Softdevices support different roles and connection configurations.
