Right Now we are using Leased Line connection which give us 13 Static IP, Since it is costlier we are planning to switch to Broadband connection. But with broadband connection we will get only One Static IP. So what I think is assign the single static IP to Mikrotik router, If any one want to connect to their office system from home they need to use Mikrotik router IP, from Mikrotik router to their system(that have dynamic IP). so here some thing like this I would expect to work,

user from home uses: systemName.xxx.xxx.xxx.xxx to do RDP to their office system. Where xxx.xxx.xxx.xxx is router IP.

So here Mikrotik router should remember which system it needs to divert the RDP access to. I guess DNS in mikrotik router would work for me to divert RDP access to appropriate system by systemName.

The setup we are going to have is

Internet -> Mikrotik -> PrivateNetwork(atleast 10 systems connected over 2 Switches)

Can anyone tell me how can I make this setup work?

If you have only 10 systems, I'd ditch DHCP on your network and statically assign addresses to all of the computers. Then you can use port mapping on the WAN interface of the MikroTik to map random ports to the individual systems. You can even register for a domain name so your employees don't have to know your external IP...they can simply RDP to the hostname and port number and get to their system.

Honestly, though, that's not a safe practice. What you should do is create a VPN to allow secure access to the corporate internal network. Exposing RDP to the Internet through port mapping is an easy way to get hacked.