@RobertQuasar Hey! Good luck with your story bro! Of course, feel free to borrow my ideas as you please my guy!
As for research for the Sacred Treasures.
The thing is... It's an issue I also had.
Eventually, I only worked out the ones I managed to find and make an obscure connection to said treasure.
There's an image on google you can check, simply write JJK Ten Shadows Treasures and you'll see what I mean.
Based on those treasures, I bent the meaning that the ability Makes SENSE in the context of the treasure.
Jeff Level 3 - Mirror Of The Deep.
Rudolph - Jewel Of Resuscitation.
Etc...
Now, as for your question on outlining the story.
I can't say I'm the best advisor on this, since I've seen much better writers have entire excel sheets with timelines, events etc...
But I do have a basic method that is simple to follow and has worked out for me thus far:
Have an outline of events that make logical sense that you WANT to happen in the future, for example:
(1) Akira finishes Academy.
(2) Akira sends info about Land Of Waves.
(3) Due to this, Team 7 goes on Custom Mission with cascading events.
It doesn't need to be something super concrete, you can build the plot as it goes.
The important thing is setting up SEEDS to stir the story in the direction you want it to go.
If you Don't do that, and an event that you want to happen can't logically happen and you force it to happen despite not making sense... That's when you lost the plot.
There were times I had to scrap events I planned due to them not making sense, which is why you need to take that into consideration, follow logic, the world and background plot and you'll be fine!