Design question

[Marcus J]

Hi,

im planning to setup a mini wireless ISP in a office space.

I have 4 public ip-nets each a /24 (can be supernetted to a /22)
I have one 5400zl and a bunch of WL420's
and a bunch of 2650.

My idea is to assign public ip's to all clients using a dhcp-server.

I need some advice from you how to set this up.

I was planning to use one SSID for all AP's to be able to roam around. and place them in diffrent vlan's each with a /24 net or smaller. BUT the WL420 won't support Layer3 roaming i suppose?
What will happen if a client roam from ap1,vlan1 to ap2,vlan2, will it receive a new ipadress from the dhcp directly or will it hang on to the old ip thus stopping it from communicating?

OR should i use all my ip-nets in one vlan with /22 mask to be able to support roaming?
Would there be problems to contain trffic like broadcast, virus, worms and so on?