Alrighty, I'll save you the "noob talk"
If take off the feedneck and look at it, it will either have a hole for the screw to go into, or a tab that the screw keeps down in place. Most likely, the Xtra 07 will have the tabbed feedneck, but I'm not 100% sure.
As for barrel length, it's all personal preference, but I'm quite partial to 12" barrels myself
As for the actual barrel, I'd reccomend the J&J Ceramic over any other one piece barrel hands down, it will save you trouble in the long run.
And if you're really going to get a Spyder, the mods in my sig are a great thing to do (or have done for you
)
Best of luck!