The effect of the unused mounting holes is cosmetic and will have no effect on the reception.
The satellite closest to true south (the highest satellite for your location Brokenburg, VA) is 77w, but there isn't any FTA KU on that satellite. I would aim for SES2 at 87w for your first satellite as it is near the center of the arc and will be easiest to locate. Use Dishpointer to find the compass reading, elevation and skew setting based on your location:
http://www.dishpointer.com/
Your approximate location information for aiming to the SES2 satellite
Satellite Data Dish Setup Data
Latitude: 38.1456°
Longitude: -77.7192°
Name: 87W SES-2
Elevation: 44.7°
Azimuth (true): 194.8°
Azimuth (magn.): 205.0°
LNB Skew [?]: 11.6°
Aim the dish to approximate compass reading 205 degrees. Identify a landmark in the far distance that aligns with this compass reading (tree, chimney, etc.)
Standing in front of the dish rotate the LNBF in the clamp CCW approximately 12 degrees and slide it forward/aft to the centered position. Slightly tighten the clamp.
With the straight edge on the vertical axis of the dish, set the elevation to approximately 20 degrees tilted back from vertical, which is 70 degrees per your angle finder (90 - 70 = 20). Here is the math: Satellite elevation angle - Dish offset angle = Angle measured on the face of the dish. Slight;y tighten the securing bolt.
Select SES2 KU in the install menu. Set the LNB LO frequency to match the KU LNB LO frequency (either 10750 or 9750/10600). Set LNB voltage to auto (13/18vdc or Horizontal/Vertical). select transponder or enter transponder: Frequency - 11736 / Polarity - Vertical / Symbol Rate 8333. See
www.sathint.com for a list of satellites, transponders and services.
While watching the Signal Quality meter reading on a TV sitting beside the dish, SLOWLY pan the dish East 15 degrees and West 15 degrees from the landmark. The Signal Quality reading will jump when the satellite signal is detected and locked. If no Signal Quality reading is detected, increase or decrease the dish elevation in 1 degree increments and repeat the SLOW East/West pan while watching the Signal Quality meter reading.
Once the Signal Quality has been detected and optimized, rotate the LNBF skew slightly and slide towards or away from the reflector to further optimize. Snug the clamp to secure the LNBF.
Perform a Blind Scan type satellite scan for all FTA channels. When the scan is complete, exit the install menu and engoy watching the programming that you just found!