I’m sure you have read this post before create this topic.
This is one point here.
The store is for apps only, not for changing the os.
A good point to use SailfishOS is the reals access to the system. You can deal as admin w/o special rooting magic. So you can play on your device every day. If you find a great new trick you can publish it at e.g. OpenRepos.
Of course. But you can help yourself with some search here or in the older together.jolla.com forum (e.g. see here or here)