Up to you man.
Personally, except for sometimes changing the E string to D for drop D, I keep my 7 string in B standard.
I just prefer the extra tightness of the sound when it's tuned to that regular tuning
Almost perfect.. the low could do with being a 60 or 61 but it's not a major issue. It's just compared with the perfect tuning stability of the rest of the strings the Bb needs slight maintenance sometimes.
it totally depends on the songs mate,i play in B standard(B-E-A-D-G-B-E) and it fits perfectly for my songs.
i suggest you to try your songs in different tunings and the decide what fits best.
cheers
Remember, you don't always have to play in the key signature of your tuning. (For instance Drop Bb and playing in Bb minor/major all the time)
My band uses Double Drop D in a custom 8 string tuning, D-G-D-G-C-F-A-D. Just because the low notes are there, doesn't mean you always have to use them
(I assume you know this already, I just thought I'd add my two cents bc I am honestly sick of hearing every song on a band's album being in the same damn key signature)