Nobody should click your HTTPS links to malware 'd JPG files. This backdoor malware doesn't rely on the normal patterns to hide its content (like base64/gzip encoding), but stored its data in the EXIF headers of a JPEG image. The malware is divided into two parts. The first part is a mix of the exif_read_data function to read the image headers and the preg_replace function to execute the content.

The functions are harmless by themselves. Exif_read_data is commonly used to read images and preg_replace to replace the content of strings. However, preg_replace has a hidden and tricky option where if you pass the “/e” modifier it will execute the content (eval), instead of just searching/replacing.

1: could i replace the disck drive with this in theory https://www.amazon.co.uk/dp/B01IH8DDBE/
No Idea

2: How easy is it to remove the heat sink drive thing taking up all the space and is it worth removing to add a rbg fan?

Its not easy at all.

3: what size fans fit in the 780 mt at the front(like this)
There is no mounting area for this and no header to power a fan.

4: will this gpu fit in the 780 mt and should i use this psu  
The Zotac 1050TI mini fits but might not have enough power.

5: what mobo upgrades can i do with out having to get a new case and has exactually the same features but allowes me to add better cpus and over cloak
NONE.

6: what is the best cpu for this current mobo

Intel® Core™ 2 Quad Q9650/3.00GHz, 12M, 1333FSB
Intel® Core™ 2 Quad Q9550/2.83GHz, 12M, 1333FSB
Intel® Core™ 2 Quad Q9400/2.66GHz, 6M, 1333FSB
Intel® Core™ 2 Quad Q8400/2.66GHz, 4M, 1333FSB
Intel® Core™ 2 Quad Q8300/2.50GHz, 4M, 1333FSB

http://i.dell.com/sites/doccontent/business/solutions/engineering-docs/en/Documents/optiplex-780-tech-guide.pdf

7: will adding an 2.5" ssd without replacing my hdd work by using these items

No.

8: what case can i change to without having to get new hardware to fit in it?

There are NONE dell is proprietary.