Uh?
First and foremostly, you can be ridiculously spread out in church worlds.
First church is mobile (or was atleast prior v7.0) it means that it can be demolished and rebuilt in like 5 minutes for like 200 each resource in any of your village.
No need to build other churches for quite some time if you are organized enough to use up it's mobility. Once you have built another church, you lose your first churches mobility and can't move it around like that.
Sheesh, you'd think after 2 years with churches this would be common knowledge, but nooo....
EDIT: This was true back in June 09. I'm not sure it is now since i've been away for so long.
I didn't know that you could demolish your first church if done before creating other (normal) churches. Good to know...
But I do want to comment, if I may. You're right that jumping around in a church world is OK, but i would recommend clustering, at least at first. This obviously depends on your tribes strength and your relative location to the core of your tribe, but overall clustering in church worlds pays off dividends. Simply put (and avoiding numerous other details), you want to cover as many villages inside of a church as possible, optimizing the steep cost of farm space for a church village. This is also why lvl 2-3 churches are usually preferred.
I also wonder about your recommendation of simply mobilizing your first church in order to jump clusters. The way you worded it, doesn't this leave your original villages churchless?? Not that this would be detrimental, but it would be extremely risky. Most of the time (but not in 100% of the cases - I would say about 0.1% of my villages in W30 are nonreligious) it's always preferred to have your men fighting at 100% strength.
Lastly, you actually can mobilize your first church once other churches are built. It's no big secret and is used a lot in mid to late world on war frontlines.
As for the question of the thread topic, it is my suggestion to cluster up early on. Again, this may depend on your relative location to your tribes core and how loyal you are to your particular tribe. Say you are far away from them, it may be wise to get a village or two next to the tribes core in the case your first village is nobled. As for barb vs. player - I always think it's best to noble out players, rather than barbs. You must be careful going about this, but from my experiences, it's the way to go. You want to find the optimal pay-off between loss in troops and nobling a village that has been built up for your benefit...usually barbs are low cost in troops, but high cost in build-up. A simple excel spreadsheet can be used to aid in these decisions.
Lastly, there are a few cases I can think of where nobling a bonus barb may be advantageous. There are a few paladin weapons that if one was lucky enough to receive as their first weapon could perhaps nicely complement particular bonus villages (assuming you had that particular bonus village near your first). This is one case where barbs can be a good idea - there are definitely bad, OK, and great ways to use those bonus villages. I have found that almost all of them are best used with special builds or particular village types.