Newbie have some questions about NetBSD

["Ling Xiaoheng" <lingxiaoheng%gmail.com@localhost>]

I'm the newbie for NetBSD,I always using FreeBSD before.Now I'm
insteresting in NetBSD.I wanna rebuild it via the source.I read the
NetBSD Guide Book,I saw there are 3 version about NetBSD source
code,there are NetBSD release branch,NetBSD stable branch and NetBSD
current branch.
If I use Release Branch,what's the different with Stable Branch,is
that like FreeBSD Standard source code,just fix some security
problems?

Should I rebuild the system via source code? or only need rebuild
kernel.I remember in the FreeBSD,when us update system we should
rebuild world and then rebuild kernel.What about in the NetBSD?

By the way,does NetBSD have any special for the CPUTYPE,In the
FreeBSD(/etc/make.conf
http://www.freebsd.org/cgi/man.cgi?query=make.conf&sektion=5) there
have CPUTYPE enabling optimisations more specific to my CPU,but I
can't find any detail information about NetBSD.

I read the chatper about Crosscompiling NetBSD with
build.sh(http://www.netbsd.org/docs/guide/en/chap-build.html), In that
chapter,I can't understand what is userland use for,is it important?
And I also can't understand with Static Builds and Toolchais.I'm not
english native speaker.Who can explain to me more easy to understand.

--
Regards

linyin.8800.org