1st question: Yes, you can manage an ESXi host directly using the vSphere Client. What you will not have are features like cloning, migration, ... which are only available with vCenter Server in place.
2nd question: You can create as many vSwitches as you want (up to the supported maximum). For the ones which need access to the network outside the ESXi host you have to add an uplink. vSwitches without an uplink can be used for private networks.
André