BIGIP DNS Domain registrar NS records

I have implemented the in-line mode. Typically, you can have 1 GTM per Region. There is typically 1 DC per region and so, 1 GTM per DC. If you have multiple DC per region, you can choose 1 DC to be the GTM DC.

Now, you can have multiple GTM in a DC, if you have more traffic and critical applications in that location, depending on your business. As a rule of thumb, 2 GTM per Region/Continent/DC is acceptable.

Example: NA - 4 DC - 2 GTM per Region for 2 in total. So, 2 of the 4 DC need not have GTM.

The exact numbers depends on your business needs. Sorry, a bit vague but hope I was able to provide some framework.