My recommendation is to start with the HD7000R antenna system install , it is simple.
And more can be added later.
Yes the coax wiring that is in place now can be used.
For splitters I recommend ,
http://www.hollandelectronics.com , also available at
http://www.solidsignal.com.
For one Tv connected use no splitter.
For 2 Tv's connected use a HFS-2D , 2 way splitter.
For 3 Tv's connected use a HFS-3D , 3 way splitter.
For 4 Tv's connected use a HFS-3D , 4 way splitter.
Are you discontinuing and disconnecting U-Verse and sattelite service Completely??