Ok, I think you've done well but I've a couple of questions myself.....
Are those channel totals just FTA or everything (I.E. scrambled, radio and data as well)?
Are you sure you need more than over 7,000 channels? I pick up about 3 to 4,000 FTA ones with my set up and never get a chance to look at them all.
Don't get obsessed by percentages. It's the ones that just lurk below lock you should concentrate on. It depends on what you really want the system for, watching tv or building up a list of as many channels as you can? Sorry if that sounds a bit harsh but you will find 80% to 90% of the channels you can get you will never, ever watch. You may be a little hampered by the lack of a blind scan on the VU+ as well. Keep an eye on the new channel thread on here and look through KOS, Flysat and Lyngsat from time to time, as Timo suggests.
Without a photo of the dish and it's LNB set up as it is now, it's hard to say if the additional sats are possible. There's only one way you'll find out.
Other narrow LNB makes are Inverto multiconnect, Alps and a Megasat multifeed. Not sure if the multiconnect will fit on your LNB mounts, maybe with adaptors. You will be restricted more by the size of the holders rather than the feedhorn diameters. If you fit LNB's that are smaller diameter they aren't as efficient as a 'full' LNB and more susceptible to rain fade and performance drop off in bad weather.