Unfortunately, the USB port on the Time Capsule, and for that matter, any Airport wireless device, are limited. See this KB article:
http://support.apple.com/kb/HT2421
Do you not have DSL or cable service where you are? Those would have much faster connections than the MiFi.
I know the MiFi device is kind of cool, but it is meant more for when you are out-and-about traveling and away from your more permanent connection back home.
That is not to say that some have not been able to create home networks with their MiFi. See the following links for some ideas, but I still don't think it will allow you to do what you have in mind.
http://www.evdoinfo.com/content/view/2911/63/
http://www.evdoforums.com/thread12871.html
Also, search Google for "MiFi home network". Cheers!