It depends on how many runways you have and, as you said, how many gates you have. The planner will allow you to plan flights at any minute but if you have three flights planned at 17:15 but only one runway you are looking at a congestion issue.
The seven day format of the schedule is of course created like that since there is seven days in a week (I know this is common sense but I like to be as clear as possible 
) . However, flights might have different characteristics where one of these characteristics is that the flight is daily, weekly, or bi-weekly. If this is the case, there will be some sort of flag on the container showing this. For example, one flight slot container might read CL123 [DAILY] and when you place that container on for example Monday at 13:37, it’ll apply for all days of the week. I’m currently looking into how this system will work, but we don’t want to limit us to only once-a-week flights or, if you’d have a flight that takes place four times a day each day every week, a UI where you’d have to manually place out 28 containers.
It depends on what you mean by a “tutorial”. Will there be a dedicated game mode where you will be guided in playing a certain world for like 45 minutes? Initially no but perhaps later. However, the first version of the game will ship with a lot of comprehensive information on what certain parts do or how they function, either in separate panels where relevant or perhaps as an in-game wiki or handbook (perhaps as a part of the management panel?).
Nope, they are simply rows that’ll allow you to schedule flights without overlapping containers. Imagine if you’d have five flights all arriving 14:51, 14:52, 14:53 and so on… would be a quite congested schedule if there weren’t any rows.