3 display questions

You can crossfire any two AMD/ATI cards assuming they are both capable of crossfire. The catch is that the total configuration will be downclocked to the slowest card. So with a 6970 + 6950, it would be as if you had 2x 6950. Also if you grab a 1GB 6950 card you'll be limited to a total of 1GB of VRAM.

The ASUS VS229H-P 158.00 while this isn't the ideal Eyefinity monitor it is a 22" e-IPS screen so you're not going to get the fading effect that TN monitors exhibit due to their limited viewing angles. Keep in mind it doesn't support swivel so portrait is out and no displayport so you'd need a dp>vga (passive) or dp>dvi (active) adapter for the 3rd. If you can push that monitor budget up to about $200 a piece the HP ZR22w really becomes an attractive monitor. It does support swivel, e-ips, and displayport.

For a single monitor yeah, it's a bit much but if you do plan on going to 3 monitors it's going to sit right on the edge of not enough.

Just a correction, only DP to HDMI or DVI can be passive. And for 3 monitors, active adapters are required, however you look at it. DVI, VGA and HDMI all require precise clock signals, which radeons can only provide 2.

It allows them to make thinner panels. Basically, the "old" LCDs have a CCFL (neon stick in everyday language) whose light passes trough a diffuser to spread the light evenly. That light passes then though the LCD matrix.
LED backlight basically replaces the CCFL with LEDs, I think placed on the border, and passed though a similar diffuser.
LED backlight probably has some reliability advantage, as CCFLs tend to burn-out in time, while the LEDs run cooler and have higher numbers, although I don't know how some being burned would affect the image.
Do not confuse with LED monitors/TVs (like the OLED TVs), which are no longer LCDs. LCD=pixel matrix which selectively blocks/passes light (well, non-monitor/TV LCD displays don't use pixels, but you get the general idea). Those are the really expensive ones.

But not having an external power supply does not mean it's passive. The DP port itself can provide 3.3V 500mA, which is about 1.6W, less than USB. So if an active chip does not need more power, it will not have an external power plug.
The exsitence of passive DP to DVI/HDMI is not even compliant with DP standard. from wikipedia:
DisplayPort is capable of directly emitting single-link HDMI and DVI signals using Dual-mode DisplayPort. VESA has issued interoperability guidelines for supporting single-link DVI and HDMI through a DisplayPort connection using a relatively simple passive adapter that adjusts for the lower voltages required by DisplayPort.

Note that they say "guidelines". They are not requirements.
Whereas the link you provided, I saw almost all of them sayng they are DP 1.1a compliant. DP port is not made to output raw VGA signals.

No...I just say that there is no such thing as a passive DP to VGA. Period. Cheap does not mean passive. No power plug does not mean passive.
And I'm saying the card cannot run more than 2 non-DP monitors with passive adapters. So if you do have an adapter that does not say active and you're using 3 monitor on 1 card, then the adapter IS active.
Update: just looked at some reports of eyefinity-working "passive" VGA adapters: they are not passive. If they say they offer a RAMDAC or DAC, then the are active. This is all misinformation spread by peopl who either don't know or don't research.