Is this a good idea? If so which should come first in the load order? BOSS puts AV first but AV still has ASIS listed as a master.

If you run them in the correct order, it should be fine. I run both.
So when repatching (after every new collection of mods), I uncheck my bashed patch, AV, ASIS Dependency, and AV (that's the order they're in, at the end of the load order).
I run Bash (having already run BOSS, of course). I activate the patch.
I run AV, and activate it. It has the bashed patch as a master.
I activate ASIS Dependency (I didn't want it in the other two patches, but I need it now.
I run ASIS. It has the last three as a master (plus all my other mods, of course!)

So far, I haven't had issues with this. I believe ASIS says in the FAQ that this is the method for running two SkyProc patchers at once.
Takes a while, especially when I'm adding one new mod, but it's worth it for the ASIS and AV goodness!


edit: Oh, and if AV has ASIS as a master, you need to run AV when ASIS isn't loaded. That should sort things.

Do I really need to wrye bash them? I thought that Skyproc accomplishes the same thing?

Sorry, to clarify that, I use bash for my other mods. Skyproc doesn't merge levelled lists. It's a tool that AV and ASIS use (have you ever run SkyProc on its own?)

Oh ok, now I understand. I don't use bash myself as I only have 1 mod that alters leveled lists so I'm not really too aware of exactly how it works. Thanks for the help =)

No problem. There are some good guides out there, if you ever decide to try it.