How to add a new IP subnet to the network?

Question

Helpdesk

Good evening everyone.
It is very necessary to consult a specialist who uses several subgrids in his network not in theory, but in practice.
There are two questions:
1) I raised the controller to windows 2012, the gateway to Freebsd (but in the future I want to buy Mikrotik)
The task is next: to increase the pool of IP addresses, because I have already used almost all IPs and there really is not enough
How to add a new subnet correctly, because in there is a lot of information on the Internet, but there is no consensus on how to do it better.
Some write that just reduce the mask and you can use the trace subgrid, others raise it on Vlans, etc.
2) I understand correctly if I need to configure access between subnets with access restrictions to resources, is this already being done with the help of Vlan and network equipment (or can it be done on a windows server)?

Answer 1

What would be correct:
And don't forget managed switches at the access level!