What is the USP of Spider Linux in comparison to every other distro?
Spider Linux's unique selling point is that it can do whatever you like but without all the cruft of something like, say, Gentoo and Portage. In fact the whole distro is based around this idea of doing everything at the simplest level. That's why we're using Python for the package manager and shell scripts and trying our best to make the simplest implementations of things.
Anyone can use Spider Linux. We have rough plans to support a variety of installation methods based on preference and hopefully have a variety of init systems as well. This is supposed to be a flexible distro anyone can use.
Lots of choice but without tons of drawbacks. You could go GNUless if you really wanted to.
I am glad you asked. Our package management system uses our package manager arachnid - you could think of it like pacman mixed with emerge/portage but 10x cooler - for installing packages either from source or from a pre-compiled binary tarball. Arachnid will be developed in the latest version of Python because the language lines up with the project goals: it's getting faster with every update, it's simple and easy to use but it also has a very functional standard library.
If you need/want to build a package from source the format will also be in Python. This allows us to be functional while reproducible which, in the modern era, is a pretty important thing. It also lets the build instructions be a format which is well known and is quite simple to learn instead of having a custom formatted build file or one which uses a shell-like format.