Hello! I’ll try to answer ur questions, although some of it might be similar to the people above 
SORRY FOR THE LONG ANSWER
-
I submitted my apps on J15, and I’m pretty sure others did too(I submitted my app to one of my schools at 11:53 PM). I don’t think it has any effect on ur actual application tho to the committee.
-
Definitely not bad to apply to 5+. I applied to about 10. But I think things work different for everyone. If boarding school is your ride or die option, it might be good to have safeties, matches, and reach schools. Always make sure to cast a wide net.
-
I’d say they take everything into account(maybe some factors more than others). Essays and interviews might be a stronger factor, because they want to see that you have passion and interest towards their school. Additionally, they want to see your character. Extracurrics are also important, but know that there are plenty of people who’ve won international awards and are child prodigies but still have gotten rejected from schools. I’d say grades have a little more weight than SSAT, escpecially with the fact that some schools are test optional. For example, I had an amazing interview at one of the schools(the interviewer made it look as if I was already accepted just from the interview) but I ended up being waitlisted(prolly cuz my SSAT was too low). Things will be fine as long as you be authentic and true to who you are in the process.
Its really good that you’re thinking about this ahead of time! I applaud you for that. I came pretty late in the process. Good luck with your applications!