Hello Alex, thx so much for answering and sorry for the late view. I was waiting on my actual email for a response (which I did not use here, lol, of course, had to be so)
My questions did mostly resolve themselves in the meantime, found everything out, except it does not work. Here is what I did and what happened.
1. it is around the 6th time I installed the core. First, it was ready but the harddisk showed only around 10gb instead of 280 like announced at install. I got nervous and did it again, really fast hard disk goes up to 120Gb, so I thought everything fine, but got stuck on 2 years 30 weeks left sync with no movement, nothing helps, no reboot, so deinstall again and so on a couple of times until I found out that you can not interrupt the program (like it happens a lot here in D.R. because of power failure. So, this time I connect to a USP power backup, but again some try to get it running with my website.

2. At this moment I am stuck at copy text from your plugin to bitcoin.conf in AppData- roaming -bitcoin. I can save the file, on start daemon, the line shows as read without error and commands prompt starts to print out 1000s of lines to sync. (this time I did not start the windows interface only the command prompt)
on refresh website then, the error message does not disappear. I don’t know, but I found a difference in your video and my site text to copy. in the video you mention rpcuser and rpcpassword, while on the website it says rpcauth=admin:aaacccd00ssblablabla…etc, I tried both ways, split like in your video related to what I filled out on settings onsite with rpcuser and rpcpassword, as also the same way as it shows on settings page. both ways no success until now. I attached what I can see, maybe you can tell me the mistake I did.
3. Something I don’t understand and maybe that’s the problem, is that I have to put in the IP of the daemon, which is the IP from the pc I installed the bitcoin core and running right now. But on the conf text to copy, that IP does not show up. How does the website know this address? Or better, that IP is a typical home network IP not the public ID which I never got asked for.
4. Regarding exchange extension, I still have the old version from my first membership here, as soon as I get it running, I play around and let you know. Mostly the reason for the need is, that we purchased some ASIC miners and I want to sell some of the production here in D.R. just for a special group of friends, and for my partner in England, so more easy to interchange with our own wallets with the lowest cost.
If you could find me a solution would be very much appreciated and again thank you very much for helping
(I xxxed some sensible data on the screenshot)