A little bit late on reading this, but...
Sam, I think you are 100% in error on your power weapon ruling. If you have to use what is on the GW kit's sprue, this would mean a space marine tactical squad can never have any sergeant options beyond a plasma pistol or chainsword? That is absurd. What is even more disturbing to me is that following this statement, you consider allowing a necromunda model to represent something? I am not sure what your intention was when you typed that. The game is obviously shifting toward a more open and casual format where the hobby has impact on gameplay. By restricting a simple weapon swap, you a restricting the overall spirit of the game, which as a judge, reflects very poorly.
My suggestion is to simply request that models equipped with a power weapon are the type you modeled them as (power axe is an axe, etc.) for the next event to ease things, and seeing how things go. It is too easy to listen to the opinionated retards on the internet about what will be broken when none of them have more than a handful of games under their belt. As far as modeling for advantage, the advantage is pretty simple, you get an option, an option that have you any marine character could pay extra points to have as well. I think you are simply afraid of too much from ramblings of people before anyone has really seen a metagame or even the basic rules develop.
As far as rulings go, it is very simple, despite sales hiccups, GW has done a pretty excellent job with the FAQ and the rulebook is fairly well-written. People, just take a deep breath, relax, grab some chips, open 'em up, and read your book and refer to errata. Its about as self-explanatory as it can get if you use a logical approach instead of instantly whining. There is no reason to run round calling things broken, or shady, or even confusing before you actually give things a chance.
