Cisco Switching/Routing :: 2960 - Choice Of Equipment For Multi-tenancy?

A client I have just taken on wishes to provide internet data and VoIP for multiple tenants in their new office they move to in a few weeks.
 
they currently have a Cisco 2811 router with a 24 port Catalyst 2960 PoE managed switch serving just their staff and one tenant company who is plugged into a single port on the switch. I dont know what the tenant has the other side of that at this time.
 
when they move they currently will provide single port access points on the switch for each tenant, so the tenant can deal with their own network LAN. The client will provide phones to all the tenants using VoIP phones on a single subnet and hosted on an external PBX the phones all plug into the Catalyst and use the PoE. the WAN is a 20mbps fibre connection.
 
The client has 16 staff, the tenants are 3 companies with 3,6 and 9 staff. They may all increase or decrease in size to a total size of about 30 or 40 people.
 
I have a few questions
 
1. should I look at Vlan setup for this instead of the current basic routing setup or is that overkill since they only use one port access point per tenant as gateway.

2. can the cisco 2811 handle this or is it a bit old.

3. what router replacement would be recommended for this task given the above info especially if I went with Vlan solution.

4. any thoughts on the current switch's capability for this task.

5. managing bandwidth solutions? is there any router designed with this in mind. the ASA maybe or something like it with nice visual webgui management capabilities for monitoring and controlling bandwidth use of tenants?
Mark