Welcome to the forum from Texas.
I will answer what I can.
PSA Gen2 seems to be a good rifle for the money from the reports on here.
For the distances you will be shooting, even out to 500 yards+, you will be well served with a 16" barrel. There is almost no benefit to a longer barrel. It will also help your desire to cut the weight.
A gas gun should recoil less than your bolt gun, so you should not need a limb saver.
I have not used the scope you have, but 8x at no more than 500 yards should be plenty of magnification.
I can't speak to the ballistic difference between the 308 and 6.5.
You should get more experienced answers in a little bit.