You really need to describe your infrastructure better. Are all the switches connected via a backbone, or is there some routers being used? Is the default data going to be different subnets for each floor also?
With answers to these question, it will be easier to make recommendations.
In scenario 1, same default data network, common phone network and backboned switches, I would just change the netmask and use lldp or central dhcp server with the Mitel option 125 to put the phones on their vlan.
In scenario 2, separate data networks, separate phone network, some routing going on between the phone networks. I'd be inclinded to setup something like vlan11 data vlan 101 voice for 1st floor, vlan12 data vlan 102 voice 2nd floor etc (this would keep the default vlan1 open as a mangement vlan). You could the use lldp and/or local dhcp to send the phone to the correct vlan where it would see the helper address and have it's dhcp sent to the MiVoice :-)
In the 3300 you would define all networks, created the dhcp address range and setup the options per subnet rather than global.
I suppose you could also have some hybrid where there is a backbone, data networks are separate but voice is just one big network.
I don't know your reasoning behind the setting up the voice as described. If the purpose is to keep thing simple, I think it becomes more complicated. I would use an extension numbering scheme per floor to do KISS
