Advice and ideas for my new desktop

1) while the fx8320 isnt bad for the price... if you want to do 3d modeling you will really want to get an i7 or a xeon which is basically an i7 without integrated graphics but with a cheaper price. if you intend to do anything complex with any sort of heavy renders this will help out immensely.

2)if you went amd what you have would work but if you went intel it would need to be changed. i'd go h97 if intel.

3)your choice... but the cougar solution is cheaper and might have better airflow.

4)16gb is fine for most cadwork including 3d and rendering most of the time. the only exception would be your super complex or huge projects but then the rest of your system would be bogging you down on those too unless you upgraded. 2x8 1600mhz cas 9 will be fine. technically if you only worked on small projects you could likely get away with but 16 is suggested. i worked for a company which only had 4-8gb of ram in systems when our projects were 2.5-3gb in size and on the lower ram pcs it definitely hung and slowed them down. the ones with 8 were fine. keeping in mind they were large projects but not highly detailed. detailed autocad projects need even more so i think your 16 is going to be safer to go with.

5)you will want to get a good quality power supply. i would recommend xfx or seasonic. a 500w would likely work however a 550w gives you a bit more headroom.

6)instead of zotac i would recommend the asus direct cu ii models, xfx models or evga models. a 750ti is going to be fine for most average cad rendering however if you need to work on anything complex or deal with huge projects and upgrade may be worthwhile such as the gtx760 or perhaps the r9-280x. the 280x is a bit more optimized for opengl (live previews of 3d) than nvidia i believe while the drivers from nvidia might be a bit better for autocad. ideally professional cards are the best... but the problem is that they are also very expensive for little gain. big corporations buy them though since they are worth the cost since paying an employee to wait on the machine costs them more.

basic line drawing doesnt need much so i will not mention that, however complex 3d projects can draw on all parts of a system including cpu, ram and gpu... while rendering is typically more cpu based while the previews on screen are gpu based. however, there are certain types of rendering as well as settings which can use the gpu for final rendering as well.

i'm a fellow cad designer and i have ran cadd/3d on various home systems including both desktops and laptops and various work systems so i have a feel for what tends to work and what doesnt. i've also been building my own systems since the early 2000's so i have a good idea of what tends to be good and what doesnt in terms of parts/branding/choices.

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however... if you are on a STRICT budget and cannot go much more than what you have now...

-get a better psu using the money saved on the case to pay for it.
-get the 8320 instead of the 8350 and a cpu cooler to overclock it a bit (more cost effective than the 8350)
-with the extra money from that bump up to a gtx760 or the amd 280x. the x is one step above the 760 in terms of performance for not much price increase though which makes it a good deal.