GTM w/o BIND and NS Records

Yes, to prevent BIND from answering queries off-box, disable it in the profile, just as you say.

In your case, DNSExpress is only providing answers to things defined locally, which means, zones for which the BIG-IP is master and authoritative. That's completely fine. There is no need to manually create the zones associated with WideIPs. When you create a WideIP, the zone is automatically created. You would add DNSExpress Zones only if you also wanted to slave from elsewhere (which you don't).

In short: you're doing the Right Thing to achieve what you're after. :)