Hi Abraham,
Answers to your questions:
Q: I want to know if it's normal that the WAAS express routers do not appear on the WAAS CM.
A: Management for WAAS Express is available through WAAS Central Manager (WCM) running WAAS software version 4.3 or above.
Q: Do the WAAS express solution support Get VPN : that is can I activate both features on the same interfaces of a router?
A: Yes you can but make sure the traffic encryption happens after the WAAS express optimizes the traffic.
Q: Beyond the waas enable command, is there anything to configure to have WAAS properly operateat the remote site?
Yes, there are couple of things you might want to cross check:
Configuring Optimization on WAAS Express Interfaces
http://www.cisco.com/en/US/docs/app_ntwk_services/waas/waas/v441/configuration/guide/network.html#wp1075272
Managing WAAS Express Devices
http://www.cisco.com/en/US/docs/app_ntwk_services/waas/waas/v441/configuration/guide/other.html#wp1062469
Hope this helps.
PS: Please mark this as Answered, if this answers your question.
Further, in the future, please post any WAAS relateds questions under WAAS category: https://supportforums.cisco.com/community/netpro/data-center/waas?view=discussions