For #2 you'd either need a new mainframe harness that runs the bar and has connectors for each row.....or there should be an adapter that takes the existing seed sensor harness info and plugs into the STMM. 

For #3, the last one I did I put them on a tray under one of the steps. Can pull it out and see everything if ever needed to make changes or check things but very protected otherwise. Either way, you'll likely mount them somewhere in the center, may need to add your own plate to do what you want where you want