A. Are black box and defaula traces same?
Yes, but that trace only captures changes realted to DDL operations, ie CREATE TABLE/ALTER TABLE etc.
B. Is it possible to capture all the queires in the black/default trace, if it does not degrade sql performance.
with the default trace, no.
With your own trace to capture DML statements, then possible, yes; but on a busy server, though you could generate gigs of logs you really don't care about, and those logs could fill up the disk and shut down your server. a trace should be targets to what you really need to capture, and not an everything trace. also note there are a lot of other functionality to consider that might accommodate whatever you are tryingh to do:
a third part log reader, extended events, SQL audit, SQL Change Data capture, adding custom triggers, adding your own custom trace, and probably more functionalities i couldn't think of offhand.
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