please help!confused mesa card and daughter boards

There are plenty of possibilities and choices, we would need more info about what exactly you need to be able to pinpoint what you would need.
You mention dual feedback, but do not mention if the servo motor encoder will be also used as a feedback device to Linuxcnc, besides linear scales. Linuxcnc can use dual feedback devices so either way it will work, but if you are using new servo drives, they usually use step/dir control inputs and have no feedback to Linuxcnc.
Personally, i tend to use analogue control whenever possible, so i mostly use the 5i25/6i25/7i92 with 7i77, and add other cards as needed.
If you go the 7i92 route, chose the 7i92M version, it can be attached directly to 7i77 or 7i76 so there is no need for a cable.
If you plan on using the servos as step/dir with their own loop closed in the drive and additionally use linear scales, have a look at 7i92 with a 7i77 and a 7i85, or just the 7i76E and 7i85. That should simplify the wiring and setup.