How do i set up a large network with more than 300 users using dhcp and ipam

I am by no means an expert, but have basic knowledge of setting up a single IP adress range less than 250. Our company was taken over and merged with another. I need to create a new domain and i would like to deploy ipam. There are in excess of 350 users and devices. So here are my questions :

1. If i create 2 scopes on one dhcp server, what will determine who gets what IP ( the 2 ranges would be 180.10.100.xxx and 180.10.101.xxx with a subnet of 255.255.254.0.
2. Do i create a superscope by combining the 2 and then the same question remains. What will determine who gets what ip?
3. I am assuming that the 180.10.101.xxx will not be able to ping or see devices on the 180.10.100.xxx range.

I will be running 2 domain controllers for fail over with both running dhcp and DNS. I've hit a wall on this. Please help.