It will be fine.. just bridge the Time Capsule and plug it in..
Mostly wireless will sort itself out.. but you can do specific setup where either TC reinforces the current wireless. See http://support.apple.com/kb/HT4260 The instructions are fine for non-apple plus apple combo.
Or just turn wireless off in the TC.
wifi hard disk?? Why do you need this.. as TC is a wifi hard disk??