Ok, for awhile, forget about your receiver...
Forget about the sync, forget about the preamble, forget about the checksum, forget about everything else. Pretend this TX is transmitting to nowhere and nowhere likes it that way...

You know how to set up your PIC, you can set the pins, etc....
You have 7 buttons, each connected to a PortB pin...
When these buttons AREN'T pressed, the pins are high, when pressed the pin is low...
Easy enough...

Write a program that does nothing but reads the state of the pins and sends that value out in a SEROUT statement of some sort.