Mirroring for offline use - best practices?

Hi all,

I'm pretty sure this is a FAQ, but articles I found on the Internet were 
either mere "recipes" (i.e. tell you how, but don't explain why), or 
bogged down in so many details that I was never sure how to proceed from 
there.


Basic situation:

There's a master repository (Github or corporate or whatever), and I 
want to set up a local mirror so that I can create clones without having 
to access the original upstream.
I'd like to set the mirror up so that creating a clone from it will 
automatically set up things to "just work": I.e. branches will track the 
mirror, not upstream, possibly other settings that I'm not aware of.

I gather that local clones are fast because hardlinked - is that correct?
Is that correct on Windows? (I can't easily avoid Windows.)


Ramification 1:

I'm not sure how best to prepare patches for push-to-upstream.
Is there value in collecting them locally into a push-to-upstream repo, 
or is it better to just push from each local clone individually?


Ramification 2:

Some of the repos I work with use submodules. Sometimes they use 
submodules that I'm not aware of. Or a submodule was used historically, 
and git bisect breaks/misbehaves because it can't get the submodule in 
offline mode.
Is there a way to get these, without writing a script that recurses 
through all versions of .gitmodules?
I'm seeing the --recurse-submodules option for git fetch, so this might 
(or might not) be the Right Thing.


Any thoughts welcome, thanks!

Regards,
Jo