UA is incredible. Your sound will be as good as any top studio guaranteed if you record in a decent room!
Apollo Quad, 4-710d (highly recommended), 2 PCIe Octos (crazy, yes) AND just about every plugin UA makes with the exception of maybe 10 or so
Cables are really important! I use Mogami gold XLR and 1/4 inch for my instruments. For my ADAT optical connection between the 4-710d and Apollo I use Audioquest Diamond (very expensive audiophile cable) 0.75M, and from the Apollo to the Mac Pro is an Audioquest Diamond Firewire 800 3M (twice as expensive as the ADAT cable, these 2 cost $489 and $950 respectively)
The 4-710d is awesome, Solid State and Tube modulation is sweet for picking the right sound for your vocals, guitars, and other instruments. I'm actually in a session right now taking a break, for vocals I'm using a Shure KSM 353 running through the 4-710d with the setting about 60-40 Tube/Solid State. Logic Pro X runs all UA plugins in 64 bit. I'm recording in directly at 44.1kHz and have tried 192. I can't use 192 because it only gives me 2 out of 4 ADAT out of the 4-710d, which is no go for drums because I need all 4 on the Apollo and 4 on the 4-710d (This can be solved by purchasing another ADAT cable, which I won't do unless I get the best one and it's too expensive to need it right now). I'm happy with 96kHz, 48kHz or 44.1kHz. I can answer any questions you may have if you're on the fence about purchasing. I'd strongly recommend the PCIe Octo cards when you can afford it because they enable you to run UAD-2 plugins without requiring any Apollo or other UA hardware.