About to necrobump this, sorry.
I'm relatively new to taking crafting seriously. Up until now, I've only been leveling it for lulz.
So, if I'm reading this right, getting the 15k GP point and using synergy to make it into a stall will get me +5 skill points. Do I need any of the other guild items? The signboard, the fang, the tools, etc. Seems they're there to give me a +1 skill mog enhancement, but do I need that if the stall will give me +5?
You need Mega Moglification: <Craft> to receive +5 skill. To be technical, the stall in your house but you not having received "Mega Moglification: <Craft>" will not give you the +5 skill. You don't need any other furnishing combined with the stall to receive Mega Moglification.