Detached Garage HVAC – GreenBuildingAdvisor

Hi all. I’m a homeowner looking to get some feedback on my garage HVAC. It’s a 2-story detached garage with a gambrel roof. Zone 5. I’m going to be doing some work on the 2^nd floor, knocking out the truss structure and installing a structural ridge beam. Once complete, I’ll have approximately 600 SF across two rooms with a ceiling starting at 7’6” and peaking at 10’. The roof insulation is in flux. It’s 2×4 top chords and I’ll either use closed cell spray foam under the deck or slap some rigid board on top. The walls will be R-20 batts (under gambrel roof sides) and R-13/R-5 side walls (rigid board will go under new siding). There are two sets of two-double hung windows at either end with three skylights (~18”x36”) in the gambrel roof sides. All the windows will be replaced as part of the work. I’ve attached a few drawings for reference.

I have an existing 18k minisplit (Daikin FTXB18AXVJU/RXB18AXVJU) that’s been a nightmare, so I’m considering other options. The rooms will be separated by a door and there’s a disparity in temperature between the two rooms at peak heat/cold use with the existing unit (when it works). Seems like the simplest path is two ductless minisplit heads, one for each room, likely with a 6k/9k BTU split with the improvement to insulation. Alternatively, I can construct chases along the floor in each room to run duct for a ducted minisplit. Will likely throw a wall mount ERV into the mix as well.

My goal here is pretty good. Ultimately this will be used as an auxiliary space for office/exercise/project purposes. Lot of buildup to a single question:  Is the extra install cost/effort for the ducted minisplit worth it? Apart from the aesthetics, I’m wondering if there is a measurable heating/cooling performance benefit or noise reduction benefit over the ductless units.

As long as I’m here, one more sort of related question. I have a “fun” backyard with a sport court and hoop mounted on the garage. The shingles regularly get hit and the granules fall on the court. I’m wondering if anyone has a thought on a goldilocks roof option for this scenario – won’t shed material on the court, won’t be overly painful/cost-prohibitive to install with the gambrel roof angles, and durable enough to withstand the occasional basketball. 

Thanks!