I have a few thoughts.
If this tree were mine, my first priority would be to repot the tree to sit it lower in that pot. I dislike the exposed roots, but that is my taste, I recognize you may like the exposed roots, or be more agnostic on it. In my opinion, leaving this tree on "stilt roots" long term will slowly create a situation where your tree will be perched on a volcano of roots. It will look awkward and unstable. The finer roots will die, leaving a few thick roots, and zones of inverse taper, making the tree look amateurish. The tree should be potted low enough in the pot that no roots should be visible. This is a young tree, in early phases of development. The roots should not be exposed for a number of years. Since junipers are pretty good about creating new roots. Hopefully, after you bury the nebari, the roots, for the next 5 years or so, a new radial arrangement of roots will develop. The roots will come off the trunk at a 90 degree angle, rather than the 45 degree angle they are now. You want radial roots like the spokes of a wheel. Junipers often never develop this full radial spread of roots. They are not like trident maples. Often champion junipers are displayed without any exposed roots. So burying the nebari out of view is not a negative with junipers. 5 years from now you can see what has developed. If nothing has, just rebury the nebari, don't worry about it, in time some radial roots will develop.
You are in Lisbon, Portugal, which means you have a more Mediterranean climate than I do. Check with local bonsai growers, but you may be able to repot now, or in the near future when your weather cools a little and the rains return. It is important that you learn the appropriate timing for repotting for YOUR local climate. Do not listen to timing suggestions from people not familiar with your immediate climate.
Repotting junipers. I never prune a juniper within 6 months of repotting. Since the feature I think you need to fix first is the roots, I would do no styling or other work until after you have a chance to repot and situate this juniper lower in its pot. Then I would allow the juniper anywhere from 6 months to a year after repotting before beginning pruning. Junipers in general do not like root disturbance. We try not to repot more than once every 3 or more years. If you can go 5 years between repotting, that is far better than repotting every other year or the most detrimental, repotting every spring.
Take your time, and source good quality bonsai potting media. Don't use an inferior mix because you are in a hurry. Take your time. Get a media mix that will hold up for 3 to 5 years without requiring repotting. This will help you in the long run.
At least that is what I would do if this were my tree. It is a nice young tree, with lots of possible options, I like it, or I would not have taken the time to write all this. Nice tree.
And remember, there are many different ways to handle this tree. This is what I would do, you don't have to take my advise, I'm not dictating what you should do, just consider my option.