The main difference between your choices is the Fronius is a fan cooled unit and the SMA is convection cooled and sealed design.
Both inverters need 150Vdc for mppt tracking and my experiance showes that you need a good 15-20 volts above this to deal with partly cloudy weather when the DC has large variations.
For the GT, you need 16, 12 volt panels to work well, so yes, these inverters would need 12 panels.
SMA is the more mature product but the Fronius has built in disconnects, either should work for your application.
Personally if this was my system and since the energy amount is miminal ( maybe 4kw day ), I would consider using an outback GTFX3048 with a small battery bank. Then you get gridtie and some amount of emergency power for a minimal differnce is costs
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