A new build ! Need your Help :)

It is fine.
The I7 will last since it has HT and can handle up to 8 threads at a time.
Waiting for the 290X makes sense both to see performance and what effect it has on prices.
Parts look good apart from PSU, I would look for Seasonic, Corsair, Antec, Enermax, XFX to name few before getting a TT.
Currently 8GB is good for gaming but rumor has it will change with your budget I would go 2 x 8GB.
Single vs SLI can be disputed but the 2 x770 is stronger than a single 780.
Need for sound cards is based on the users demands onboard is sufficient for most.

IMHO you should get a 2x4GB Dual Channel Memory Kit like this $63 Mushkin kit:

http://us.ncix.com/products/?usaffiliateid=1000031504&sku=54963&vpn=996776&manufacture=Mushkin%20Enhanced

Your build is reasonable, and will work.
I might do things differently:
1. Since few games use more than 2-3 cores, the hyperthreads of the 4770K are largely irrelevant. Save the $ 100 price premium and use a 4670K.
2. I think Sabretooth is overpriced. Most any Z87 based motherboard will perform the same.
3. Ram is ok. no game will use more than 2-3gb by itself. Buy the low profile version so you can clear any coolers.
Ram is cheap. I have no problem with 16gb. Windows will keep more code in ram available for instant reuse. I think it makes your pc a bit more responsive.
4. Consider upping the ssd to 240gb and deferring on the hard drive. 240gb will hold the os and a fair number of games. It is easy to add a hard drive for storage later if you need to.
5. GTX780 is as good as it gets for a single monitor. I would wait on the R9 290X. At least until unbiased benchmarks including frame delays and reviews are out. It is a newer tech, and I expect driver issues for a while.
Here is my canned rant on planning for dual cards:
-----------------------------Start of rant----------------------------------------------------
Dual graphics cards vs. a good single card.

a) How good do you really need to be?
A single GTX650/ti or 7770 can give you good performance at 1920 x 1200 in most games.

A single GTX660 or 7850 will give you excellent performance at 1920 x 1200 in most games.
Even 2560 x 1600 will be good with lowered detail.
A single gtx690 or 7990 is about as good as it gets.

Only if you are looking at triple monitor gaming, then sli/cf will be needed.
Even that is now changing with triple monitor support on top end cards.

b) The costs for a single card are lower.
You require a less expensive motherboard; no need for sli/cf or multiple pci-e slots.
Even a ITX motherboard will do.

Your psu costs are less.
A GTX660 needs a 430w psu, even a GTX780 only needs a 575w psu.
When you add another card to the mix, plan on adding 150-200w to your psu requirements.

Even the most power hungry GTX690 only needs 620w, or a 7990 needs 700w.

Case cooling becomes more of an issue with dual cards.
That means a more expensive case with more and stronger fans.
You will also look at more noise.

c) Dual cards do not always render their half of the display in sync, causing microstuttering. It is an annoying effect.
The benefit of higher benchmark fps can be offset, particularly with lower tier cards.
Read this: http://www.tomshardware.com/reviews/radeon-geforce-stutter-crossfire,2995.html

d) dual card support is dependent on the driver. Not all games can benefit from dual cards.

e) cf/sli up front reduces your option to get another card for an upgrade. Not that I suggest you plan for that.
It will often be the case that replacing your current card with a newer gen card will offer a better upgrade path.
The Maxwell and amd 8000 or 9000 series are due next year.
-------------------------------End of rant-----------------------------------------------------------
6. I am not in favor of all in one liquid coolers. They are expensive noisy, and less reliable, and cool no better than a good air cooler.
If your case permits, look at a noctua NH-D14 or Phanteks cooler.
Google "H100 leak"
7. Thermaltake quality may be iffy. Look first to Seasonic for quality. 600w will run a GTX780, but I have no problem overprovisioning to 750w.