20 moa bases give you 20 MOA of elevation built in. So if your 900 yard zero if 50 MOA up then with the base you only have to click in 30MOA. That gives you more room to move and adjust the scope. For your shooting you don't need it.
Dteed came up with a very good point that I forgot about (OLD AGE SUCKS).
Yes I too keep my scope as close as I can to the barrel.
With the base yes go with the lowest ring possible.