If i use some pkg from slackbuilds say xvkbd,unrar,etc.,
I use some other pakgs from alien say openjdk,iced-web,etc.,
I use some othr [kgs from rworksman,and some from slacky.eu say MATE
Will mixing pkgs among third party repos cause trubles?
And what is best 1.Installing prebuilt txz pkgs from third party repos or 2.Building from source code from third party repos(alien repo offer both)

as long as you don't install same packages from different repository, it should be OK
i used packages from SBo, AlienBOB, and self-compiled packages and it's fine here

Aren't you satisfied with answers you received in this thread or in that one?

As for your last question that's just a matter of personal preference, provided that you trust the package's provider.

As I trust Alien Bob and am a bit lazy I tend to install his packages instead of building them.

But I would build a package if I needed to set the configure options differently, for instance to get a feature not included in the package shipped.

To check you could type; "./configure --help" at the root of the source tarball and compare the output with the configure options in the SlackBuild.

Will security patches be available for packages in slackware extra(Official) Eg bittornado will recieve security patches from slackware officially or not?