I would recommend at least double, if not triple, the capacity of the actual lawn area. This reduces travel times. We have about 300 sqm and the 1000 model, so it runs 5 days a week from 8:30 to 15:30 according to a Gardena-led schedule. If it were smaller, the travel times would be significantly longer because it would need to be charged more often.
The Gateway is quite practical. You can adjust the most important settings from the garden table, practically from anywhere, and don’t have to walk to the mower. Quite simple, for example, if you want to send it home due to sudden heavy rain. The schedules/zones can be created very easily through it, and things like weather or [sunrise] and [sunset] can be taken into account. Also practical is that you receive notifications if something is not working properly. For example, if the mower gets stuck somewhere, a cable is damaged, or the mower can’t find its station. I’m glad we have it, but it’s certainly not a must.