try every possible way to keep the piping short. and not keep the outer on the roof. keep at place where easily accessible and cleanable. keep pipe as short as possible to avoid undercharging. normally upto 15 ft is covered by pre charged gas. above that, a specific gram / ft needs to be added.
how much is the ac used. if used one or two months, let the non inverter stay. if used daily 10 hours, than inverter is good to go. get the AC which has the most air flow rate