From my experince here's some advice, also spend some time thinking about the location for the outside unit. I regret moutning the compressor/heatpump on wall brackets. The unit does make noise and vibrates enough to hear through the wall (brick, 2x6, insulation, drywall). I have a tackle bench in my boat house and the outside unit is on the wall directly behind the bench. When I am sitting at the bench, I can hear the noise/vibration too clearly. I will try to add some dampening (rubber feet) to the compressor when the snow melts in the spring. Doing it again I would install on the ground several feet from the building.
Another thing which I would do differently would be to install a piece of stainless steel to the wall before mounting the blower unit. Mini splits need to be rinsed off and cleaned every year to avoid mold/smell issues. Amazon sells bags that will contain the drippings and overspray, but staining the painted walls is still a possibilty. If the stainless doesn't match the decor, painted steel (think exterior cladding without ribs) or even melamine would be a perfect choice too. A piece bigger than the interior unit would be cheap and easy to install in advance.
Lastly the interior blower needs a condensation drip tube. Draining this tube should be part of the thought process.
Don't get me wrong, I absolutely love my mini-splits. I have one installed in my garage shop and another in my boat house. I would give up morning coffee for a year before giving them up!
