Not sure how this relates to the setup that Browan sends its devices out - but there is generally some similar band plans for those that share borders as radio waves don’t have passports. So nothing to read in to this fact really.
This will enlighten:
https://avbentem.github.io/airtime-calculator/ttn/eu868/15
No, no one said that. Try to slow down the conclusion leaping, there’s so much going on in LoRaWAN you’ll get tired very quickly.
No. The gateway is a dumb box that does what it’s told, it’s all driven by the Network Server based on the settings you’ve made. SF12 provides some benefit for contacting a far away devices if coverage is an issue.
I’d really suggest you get the kit working before looking at the esoteric options.