Server.app already includes the mod_wsgi module and a default mod_wsgi webapp example at /Library/Server/Web/Data/WebApps/hello.wsgi. It's best to leave these as-is and duplicate the files to add additional sites just in case you mess up the config.
Decide where to store your site preferably in the Sites folder. You are right about editing the files you mentioned, however copy and rename them to something like httpd_wsgi.maasaamiichii.conf. Edit that file to set your own WSGIScriptAlias, for example
WSGIScriptAlias /WSGI /Users/maasaamiichii/Sites/WSGI.wsgi
Also edit the .plist file changing 3 keys to your own stuff to match the .conf file. This file should be edited in XCode and remember the ownership has be root:wheel 644 to run. After adding these files you may need to restart the server and/or Server.app.
Next edit the file at /private/etc/hosts to include an entry like
127.0.0.1 maasaamiichii.dev
This so your browsers know the domain is on your devbox machine.
With these steps done, open the Server.app and select Websites in the sidebar. Invent a website name, let's say maasaamiichii.dev is your devbox name and maasaamiichii.com is your internet name. Path needs to match the WSGIScriptAlias path above. Select "Advanced Settings" and enable the middle 3 options (htaccess, folder & cgi). In the bottom box select the Python WSGI webapp to run on that site. Save and you are finished. Back on the front window you can see your website by clicking the lower right corner link.
Please note that the default mod_wsgi as included at
/Applications/Server.app/Contents/ServerRoot/usr/libexec/apache2/mod_wsgi.so
runs the included Python version 2.6? and as such is outdated. Python 3 scripts may not run without custom building mod_wsgi. In addition, the included mod_wsgi is built for "embedded mode" and so the example script forgets all data between threads. To make it remember values persistently the module needs to be compiled for "daemon mode". So depending on what your purpose is for this website, the default config may not be enough persistence.