Help with Sister's First Workstation

Modern i5 processors render in premiere and handle the adobe suite quite well. I wouldn't be concerned about it being inadequate for a good amount of time.

Here is what I would get.It's from PC Case Gear, a company that I trust. https://www.pccasegear.com/index.php?main_page=wish_lists&wlcId=537713&action=wish_lists

i will look what i can put together for that budget.
But if you could afford intel then just do it.

He can easily afford Intel at that price but with Nvidia is a major no.

Well the Aussie prices are terrible right now.
I just looked at some of the mainstream i7´s, but they are expensive.

Hey I'm Aussie here. yeah its terrible a low end i7 cost about $430 give or take and the i5 is just plain stupid. An i5 4460 is about $275, i5 4690k is about $330. Oh how I love that our Dollar is poop right now. The only thing that is reasonable-ish is the i3s price wise here. They go for about $130

I was looking at the Xeon E3-1231-V3 which is $370,- in Australia.

20$ used can vary, but where I live you'd be able to get a HD5670 or such fairly easily (meaning a GPU with 1GB of GDDR5 VRAM). What I said is that buying a 280X is a waste of money, which on a budget like this, it is. To this your comment was "windhero is plain wrong". If you ment to say "I dont think a 20$ used CPU is good enough", that's what you should've said. Upping from 20 bucks to 100$ to 200$ you will find that there is not much of a difference. And then the difference will only be noticeable with certain things that support GPU acceleration such as scrubby zoom, pan, etc.
For complete lists:
Premiere Pro

CUDA, OpenCL, Mercury Playback Engine, and Adobe Premiere Pro

Photoshop
https://helpx.adobe.com/photoshop/kb/photoshop-cc-gpu-card-faq.html
Lightroom
https://forums.adobe.com/thread/1828580?tstart=0

Based on my own experience using photoshop daily with a laptop with an integrated Intel HD4000 GPU and at home on a desktop with a 980TI, the difference is there but probably not worth the around 700€ difference in cost that I'd estimate there to be between these GPUs (if it was possible to price an integrated chip).

With a cheap GPU that can drive the monitors being used, a good processor, as much RAM as possible and a scratch disk you'd be much better off than cutting from any of the aforementioned parts in order to get a 150-250$ GPU. Every penny you save on a GPU buys you more RAM, more storage, bigger/better/more reliable scratch disk etc. And as said, the GPU is easily upgradeable and usually for quite cheap too if buying used.

Can I just throw out the curve ball...

Why do you need to buy new? You can always pick up a bargain with older products with reseller warranties, for example you could get hold of HP z600 or z800 workstation, Lenovo C20 or D20 Thinkstation cheap enough giving you lots of extra funds to like add more RAM or a high end GPU or even buying better quality screens.