Hi Bart.
Large solid tanks in the greenhouse are fine as only the top of the water will gain the most heat, thousands of people place inside or outside, it really depends on space.
Please take a look at the brochure as pot size is really a matter of choice. If you visit AutoPot Watering Systems FB page you will see we ave been growing tomatoes in 8.5ltr pots for 12 months, we use either this size or 15ltr pots.
You simply set the Ec in the reservoir once and that is it, pH can also be set, remember there is no recirculation of fertiliser so levels do not alter once set.
Oh and thanks for the compliments.