I7 K system, solid or should I save and upgrade more?

For gaming, the graphics card is the most important component.
I would suggest this GTX670:
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

PCIE 2.0/3.0 is irrelevant. No graphics card now pushes the limits of 2.0, let alone 3.0.
If you run sli, the slots will run at half speed, X8/X8, and even that is not really a problem.

Today, there is not much value in upgrading a current sandy bridge cpu in favor if an ivy bridge cpu.
But, for a new build, I would definitely go ivy bridge. 3570K.

How relevant "I also like to play in PS, Vegas, and Flash" is, I can't say. How is hyperthreading important to that?
If it really is, then look at the 3770K. But the current 3570K is one heck of a good cpu, and I doubt that you would find it lacking. It is 5% stronger, clock for clock than sandy bridge, and certainly less expensive than a 2600K. Use that trade off for a GTX670, and your gaming will be much better.

You will be able to run triple monitors, and then decide if you need a graphics upgrade. The GTX670 is so close to the GTX680, that it would not make sense to do that. Your choices would be to spend another $400 for sli, but that would require you to buy a more expensive motherboard now, along with a more powerful psu on speculation. I suggest planning on selling your initial card and replacing it with a single much stronger card. Today, that is a GTX690, a very expensive card. But, in total, not to different from sli.
More likely, the real Kepler top end card will be with us by the end of the year, making that the triple monitor gaming card of choice.

You have picked expensive motherboards, primarily to plan for sli. If you will upgrade via a single graphics card route, you are looking at cutting that cost in half. Even a M-ATX motherboard will do. Actually, other than graphics, how many of the expansion slots will you actually use.

My short list of quality psu brands would not include thermaltake.
I would look first at Seasonic, Antec, PC P&C, Corsair, and XFX.

You have picked a very expensive case. If you love it fine. But, realize that you can buy a equally well cooled and competent case for half that.

I do not much like the all in one liquid coolers. They are expensive, noisy, and in a well ventilated case, they are no better than a good air cooler. In fact, they may cool the cpu well, but the hot air gets dumped into the case where it heats up the graphcics cards. Save a bunch, and get a $20 cm hyper212. If you want the best $85 buys you a Noctua NH-D14.

For gaming, 8gb is fine. If you will be running 64 bit enabled apps, then 16gb is good. Ram is cheap.

Your link to to the monitor is wrong. Regardless, I think you can do better on the monitor. I think 21.3" is a bit small.
A monitor is one of the more "future proof" items you can buy.
If you are going to triple monitors, consider buying them all 3 at the same time. That way you will know that they match.
As a added thought, why not consider a 27" 2560 x 1440 type monitor and forget triple monitors?

How much hard drive storage will you need?
A 120gb SSD will hold the os and 6-8 games. Start with that, and add a hard drive for storage later.
If you do not have a need for hard drive storage for large files like video's, get a 180 or 240 ssd and be done with it.
I suggest Intel 520 series or Samsung 830 series for reliability. You will pay more for them.
From a performance point of view, all modern SSD's perform about the same for normal desktop and gaming operations.
Once you have one, you will never build without a SSD.