Design and create Vlans onflat network

Need to VLAN a flat network.  
I currently have a network and it is one large flat network with one subnet of 255.255.252.0 with a range of IP's 192.168.0.1 - 192.168.3.254.
All of my servers, routers firewalls, printers , copiers  and switches are within 192.168.1.1 - 192.168.1.254
My Workstations (Windows 10 )  are all receiving IP addresses from DHCP server and in the range of 192.168.2.50 - 192.168.2.250

I have been tasked with setting up vlan's for the entire network to improve security and performance

I currently have a 5 switches which are all 48 port switches and in  a stacked configuration with 40 GB uplink to a "Central" Switch. These 5 switches are considered our user segment which has workstations and Printers connected.

The Central switch is actually two 48 port switches that are stacked and have the Servers, routers and firewall connected.

my default gateway is a cisco Switch .

I'm looking for some guidance in multiple areas,
1. design ? how many Vlans , do I use vlan 1 ? I think my current configuration would mean everything is VLAN 1
2. Will I need to change my IP addressing of my enire network ? if so what would my new IP addressing look like. how would I g about changing without taking down the whole network.
3. Can the job be done slowly ?
4. Can a server ( DHCP ) on one Vlan provide IP Addresses toWorkstations on a separate Vlan ?

Thanks for any feedback