For the quarterly! VAT advance return (which you can’t avoid even with hobby activities, unless you have too much money to spare and don’t want the VAT refunded) I always need about 15 minutes. And you only save the income surplus calculation once a year. Since you’re doing your taxes anyway, you can also provide three more numbers.
So: fill the roofs fully and don’t let artificial obstacles stop you!
I can’t say it often enough: EVERY photovoltaic system is too small!
Example: Bad weather --> 10% system performance. What do you want to get from 1 kW on the roof?! You can’t wash laundry with it, let alone charge an electric car twice!