Hi as_m,
1- You cannot make the SRX serve as a DHCP when it's in transparent mode: See page 4 on this PDF document:
http://www.juniper.net/techpubs/en_US/junos12.1x47/information-products/pathway-pages/security/security-layer2-bridging-transparent-mode.pdf
2- The trunk interface in the SRX should be added to each different zone; Your zone configuration should look like this:
[edit security zones security-zone]
set sales-zone interface ge-0/0/1.10 host-inbound-traffic system-services [all, X services]
set support-zone interface ge-0/0/1.10 host-inbound-traffic system-services [all, X services]
set management-zone interface ge-0/0/1.10 host-inbound-traffic system-services [all, X services]
3- You said and I'm quoting "I notice these CLI commands don't create an entry in the vlans section. Is this necessary?" . I'm not sure if I understood you , but those configuration does not require any additional configuratio in the SRX under the [edit vlans] hierarchy.