1. I might actually prefer number 3 or 4... I'm a tad bit OCD, and having that gaping empty space while not in a raid would eat at my brain.
I also love to have everything pretty close to centered/evened out. This creates a sense of balance visually and is not distracting. Also, I couldn't *really* tell, since your camera was zoomed in in that first screenshot, but I would suggest a viewport since your background frames are so thick and opaque.
2. I use Bartender3. You can get it here or at wowace.
3. I have Antagonist and Chronometer, but my husband prefers nECB. I haven't tried nECB personally, however.
4. As for FuBar plugins.... I think the basics are a must have: bags, money, durability, performance, clock, volume, etc. FactionsFu is nice if you're tracking rep, FuXPFu places a pretty xp bar as a border on your FuBar (it can also track rep), GarbageFu makes it easy to dump those grays at a vendor, MailFu allows you to dump the mail icon around your minimap if you're moving/customizing your map, MicroMenuFu puts your character/talents/spellbook/etc menu up in FuBar, PetInfoFu for hunters/locks, TopScoreFu to keep track of damage records... I use a few more than that, but those are the best, I think.