Hello,
You don't have to create new routes for every IP in the subnet. What you should do is not an IP-to-IP routing, but a Network-to-IP route. So, in this case we would route the network 192.186.2.0/24 to go trough 10.5.2.1, so this means that every device which is in the range between 192.186.2.1 to 192.186.2.254 is going to be routed trough 10.5.2.1.
For this scenario, it wouldn't make any difference to use fixed IP addresses or DHCP for the LAN devices, as long as every device is configured with the Gateway 192.186.2.1.
A diagram would help me to understand the setup and give you more precise answers.
Best regards.