Welcome to the discussions!
You told us that you were having "major issues", but did not tell us specifically how you are trying to configure the AirPort Express, or what service you want it to perfrom on your Home Hub network, so providing a step by step guide is not possible without a bit more information.
Can you clarify on this, please?
In regards to configuring your Time Capsule to "join" the Home Hub wireless network, do you understand that the ethernet ports on the Time Capsule are not enabled in this type of configuration, so you will not have the option to back up large files or make initial backups using an ethernet connection?
In order for the Time Capsule to "join" the wireless network provided by the Home Hub router, you willl need to know (or be able to locate) the exact type of wireless security settings that your Home Hub is using. The Time Capsule must be provided with this information in order for it to "join" the wireless network successfully.
Can you provide this information, or if you do not know, check with your service provider to obtain this information? We cannot proceed with the configuration until we have this information.
If you are able to locate the Time Capule near your Home Hub and establish a permanent ethernet connection between the Home Hub and Time Capsule, you will be able to backup using the Home Hub wireless network and also have the option to backup using ethernet if you wish. In addition, this type of installation is much simpler to configure (and more reliable in operation in my experience) and we would not need to know the type of wireless security that the Home Hub uses if you choose this setup option.
Please post back when you have an opportunity.