So I install yum, download what I need to build Asterisk, remove the downloaded packages that I no longer need so stability remains and I've got what I want ?!
Yum is already installed by default and should not be removed from SME Server.
Did you at all read the information that was provided to you as well as the useful links available in those pages? Keep in mind that for you to run SME Server you need to invest a little to gather your information, we can provide bite size chunks but it most off the times comes for lump sums of money.
Every advice and tip in this community is given free of charge, but if you like there are enough people here that can also provide you with payed support. So please try and dig up and digest the information and then when you get stuck or have concrete questions get to th right board and ask your questions there.