Ahlan BOBOS ANAS,
I am very pleased to help if I am able.
1. Yes, 16GB of RAM is very useful for the programs you will be using. Then, you may have several programs going at the same time. I often have 4 or 5: word processor, 2D CAD, 3D CAD, Photoshop, Internet and so on. Before you buy the RAM, have a look at the motherboard manufacturer's website and find the list of approved, tested RAM. My preference is for Samsung, but make sure the model you choose is known to be good with the motherboard.
2. My preference would be to use the Intel Xeon system with a Quadro graphics card. Choosing between NVIDIA and AMD is complicated today. The AMD cards are in some ways better performance for the cost, but both Autodesk and Adobe- also Solidworks- benefit from CUDA acceleration:
http://www.nvidia.com/object/quadro-design-and-manufacturing.html
Still, you may see from the Autodesk site that they certify Firepro and Quadro and even a couple of GeForce GTX for 3DS Max:
http://usa.autodesk.com/adsk/servlet/syscert?siteID=123112&id=18844534&results=1&stype=graphic&product_group=6&release=2014&os=32768&manuf=all&opt=2
However, I think a workstation card (Quadro or Firepro) is important because there may be a program among the many that must have it.
Given the complex programs you use, a very fast graphics card with a wide memory bandwidth and a lot of memory is important. You mention that you buy everything new, but if you are adventurous, you may consider buying a used Quadro or Firepro. Look for a card with the least use, but they are made to run at full speed all the time. I have bought eight used Quadros in the last 12 years and never had a failure. One used card (Quadro FX 580) is now 10 years old and still works perfectly. Importantly, the cost is very much reduced. I bought a Quadro FX 4800, that when new cost $1,300 and when it was 1.5 years old I paid $150. The Quadro 4000 I have now was new $750 and I bought it with no use- still in the sealed bag for $290. If you could find a Quadro 4000 within your budget, that would be a very good choice for your uses. Even better is the Quadro 5000- faster, more memory, and importantly is a double height card and so runs cooler. The Quadro 4000 is single height and runs a bit hot, especially when rendering. If you decide to buy an AMD card, have a look at the Firepro W5000 or if used, a W7000. When I bought my HP z420 at the beginning of the year, it had the AMD V4900 and over a month I thought this was a very good card- excellent for the price and would be good if you are buying a new card. I changed to the Quadro 4000 because it works better with Solidworks.
3. Yes, the kind of system we are discussing should be quite good for the programs you mention- really any kind of image making / processing.
4. It is possible to use a quite compact case with this kind of system. However, if possible I think it is better to have a larger case for several reasons- more room for large graphics card, easier to work in, to assemble, but very importantly, it makes good air circulation for cooling easier. When rendering /processing, both the CPU and GPU may be working on all cores and at full speed. I was running renderings a few months ago and discovered that the CPU running on all 8 threads was 85C and the Quadro 4000 was 105C- too hot. This was in the HP z420 which has a large case and that could be purchased new with a Quadro 4000. Heat is a workstation problem- especially rendering and film editing/processing, so I like to have a lot of air especially when living on the on the edge of a desert- for me the Mojave in California/ In July, 2009 in Los Angeles where I lived the temperature was once 119F (48C) and I think you may also have a similar situation!
I wish that I did know more than 10 words of Arabic- one of the World's very important languages. I had some good friends from Egypt when I lived in London and other languages to me are just amazing. And, of course, Egypt has an amazing history- someday I'll see the Pyramids.
Yes, let me know what you decide to do.
Salam,
BambiBoom