How can I make my application behave well while monitoring hundreds of real-time devices?

I need to develop a real-time (i.e., info is requested and received at least once per second) monitoring application in Delphi, which monitors multiple remote devices (can be hundreds). The communication is via TCP/IP.

I am looking for advice to develop this app avoiding 100% CPU consumption and minimizing the amount of RAM used. In other words, I want my application to remain responsive and not block the system or consume all resources.

My main concern is about using threads for monitoring each remote device. Is there a limit to the number of threads my application can create? Can the threads can be started using a low or medium priority to minimize the CPU consumption?

Advice about optimal memory usage is welcome, too.