Site-to-Site VPN is used to connect usually two locations allowing multiple subnets to flow in between, although some VPN technologies like DMVPN also allow multiple sites
Remote acces VPN  is for users to gain access remotely to a network from their computers
Remote access VPN is generally broken down into Client and Clientless.
 - Client is when a client software is required to be installed on user computers, for example, Cisco AnyConnect
  - Clientless is when no client software is needed and users would access applications/network over web browser.
I am assuming you meant Clientless as opposed to classless.

Number connections depend on type of VPN and hardware platform. ASA has max number of concurrent remote and L2L VPN that you can look up on datasheet. Some router also have similar metric list on their datasheet as well.