Install the baseboards. Measure between the corners, then cut pine 1 x 6 to fit the space. Check for level, then use a pry bar to adjust as needed. Secure to wall with 2" trim nails. Work around the room to attach baseboards until completely installed.
Figure out the height from the top of the baseboard to the ceiling. Determine height of plank. Divide the height of wall area by height of plank. This will determine if you need molding installed near the ceiling. If the gap at the ceiling is greater than 3-1/2", simply rip the paneling to fit. Install without top trim. If less than 3-1/2", add trim for 2 x stock to fill the gap.