Newbie have some problem in 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