The NSA has released a VPN called goSecure. I have not tried it. Unfortunately the VPN craze has made it very difficult to locate information on creating your own. You might also look into a hardware solution. Higher end and prosumer routers like the ubiquiti edgerouter series sometimes have built in vpn portals.
Question 1: try "IP tunneling",...
nginx is the way to go. You said you do not want to be bloated, that's why I did not answer apache server.
Most companies are switching to nginx for this reason.
Either way shoul should be fine. Both are secure and high available.
Also, I see they are available for linux, but Windows Server is better as far as I know for this things, because of performance.
I think the best software for your needs is indeed Geogebra, I personally prefer the classic web version. Geogebra is like... the most user-friendly graphing calculator that I can found; other graphing calculator software can be equal or even more complex than Geogebra.
If you want to get the most of it, eventually you will need to learn how to use it like a ...
It is build from scratch, uses pacman and Octopi as software managers. It is rolling but very stable — in that, and other aspects, similar to Solus — and completely focused on Plasma. Uses systemd-boot as boot loader. Looks like "the one" for now.
Feren OS is based on Ubuntu with a pseudo-rolling-release nature, ...
XNView MP cover most of your requirements: run natively on Linux, visual, you can reorder images by drag-and-drop, you can view image on full size, can create slideshow on desired order of images (so you do not need to rename images, just play slideshow).
The Open source guide suggests Ginco, koha, openflora and pmb. I would have thought that e-prints or DSpace have something along those lines.
If you find nothing that scratches your itch, there is a Perl module that will help you build what you want.
I didn't find some program which did fit all my needs, so I wrote a CLI player to remedy this, which has these features:
hot reload, even when playing;
can move forward and backward;
can restrict the play zone precisely, in order to work on a part of the score;
auto-return mode (go back to where the play started after pausing).
Here is the repo,...