Yeah definately do both at the same time. Stretch those ligs as far as you can possibly take them, and then slam the tunica. After getting about 1/2" in lig gains with a starting LOT of 6, I maxed the lig gains out. I then took a 2 month break, came back for a month hitting the ligs hard, getting no gains, and have now moved on to tunica stretching. Gain from the ligs while you can is what I say.
Also, I do not believe girth gains inhibit length gains. My best length gains came when I was also gaining 1/8" of girth per month (the greatest incremental girth gains I have seen for myself). So basically, do everything and with as much frequency and intensity as is needed to grow!