As any question asked: How do we deal with ... think like that:
Why to reinvent the wheel in 2019? No need for it. Just look how the leading plattform has done it.
You do not have to create the whole world new.
1) Wordpress automatically changes symbols not latin into something else. With a plugin, the german ä will change into "ae" - that´s it.
2) If the title changes - then wordpress leaves the permalink as it is - until you change it be your own.
It is possible to change the Link evertime the title changes or write a permanent remove for each link is changed.
3) SEO is absolutly what should be in focus when it comes to articles. As for my own i decided to use Wordpress inside/embedded into UNA - because the lack of SEO functionallity. It´s a bitter pill to do so.
Also you can take a look on how this problem is solved in phpBB boards. They already have the answer you are searching for. 
I have seen a lot of good things disappaer in www because the boxed thinking that is sticked to the own development. But there is no need to, - you can looks how others has done that and learn from it.
Please don´t feel offended by my article - i only wnat to show a way to do that.
Best wishes and Greetings!