wow. Lucky you with such a long growing season!

For deciduous trees it is fairly normal to have multiple trunks in the canopy. I know my trees have them here and there. So I would not worry about it.
What you should worry about are the clusters of branches in the top of the tree. Everywhere where you have splits of more than 2 (So one branch turning into 3, or the trunk having 2 sidebranches at one point) you should think out to return to 2.

At the moment that might be a bit much to deal with for the plant. If it were mine, I would let it grow extensions of say 20+ cm (Maybe 5+ pairs of leaves) before doing anything to it. At that point if you prune the branches away that should go, and you defoliate the tree should respond with a florish of buds. This is however tricky: You need to judge the health of the tree.

SABonsai wrote:

It's BonSan liquid from Crespi Bonsai, should be good, I just don't want to burn the tree.
Whereabouts are you in Italy? Milan has had some really warm days. My tree has been outside on my balcony, first started budding mid-February together with my Metesequoia forest. In fact, all the plants on my balcony got leaves in Mid-Feb (Roses, Wisteria, Blueberries). Its been really warm! Winter ended in Milan in Jan for sure.

I’m actually next to the Slovenian border (so maybe 300-350 km from Milano, driving-wise?). Lockdown is kinda the same but situation is certainly way better.
We did have good weather too, and plants did wake up early (as I said somewhere else, I did repotting in the first half of February, that is definitely early) but foliage didn’t start appearing until about 10 days ago.

I think you can use that fertilizer with its nominal doses, but there’s certainly nothing wrong if you decide to water it down a bit more for the first couple of applications.

@leatherback Thanks so much for the advice! I'm happy to hear that I shouldn't worry about the twin trunk that I am going for. I've been really pondering it a lot these last few days as I really love it!
I am indeed concerned about the cluster at the top, wasn't sure how best to approach it though. I will heed your advice and just let it grow out a bit and then prune them later. As you say, I have a long growing season so all should be good! Thanks a lot!!

BofhSkull wrote:

I’m actually next to the Slovenian border (so maybe 300-350 km from Milano, driving-wise?). Lockdown is kinda the same but situation is certainly way better.

I think you can use that fertilizer with its nominal doses, but there’s certainly nothing wrong if you decide to water it down a bit more for the first couple of applications.

Ah, ok, so around the Trieste area then. Definitely a lot better that side, but I think the whole world is going into lockdown now. I am going a bit nuts not being able to go out, even just for a quick walk for some fresh air and exercise! I've been working from home for a month now... great for Bonsai and family! Enjoying it a lot actually.

Thanks, I have given it some fertiliser this morning. The guide says once every 8 days... I can just follow that, right?

SABonsai wrote:

Ah, ok, so around the Trieste area then. Definitely a lot better that side, but I think the whole world is going into lockdown now. I am going a bit nuts not being able to go out, even just for a quick walk for some fresh air and exercise! I've been working from home for a month now... great for Bonsai and family! Enjoying it a lot actually.

I've been working from home for almost a decade now, so except for not doing any business travel (had at least 4 conferences I was supposed to attend cancelled so far already, and more are certainly coming) and having the rest of the family at home with me, I can't say this is impacting my lifestyle that much

SABonsai wrote:

Thanks, I have given it some fertiliser this morning. The guide says once every 8 days... I can just follow that, right?

A lot of "how much to fertilise" depends on what you want the plant to do. But yours, right now, are in a very early stage, and you want them to build strength first of all. So sure: go with what the bottle says.
Meanwhile, understand that what you have are not really bonsai, just trees in a pot (in general, that's true for almost every plant that doesn't cost like a small car).

Bringing them to become bonsai will be your job, understanding what you're supposed to do to them and applying such techniques every year from now on.
So my suggestion is: focus on building knowledge about your plants and how to keep them healthy first.
Use that time to study what the techniques are about and what their goal is. This will include how much to fertilise, when and how.
Then try applying them to your trees; when you have a good grasp of them, you can start making plans on what your plants can become through those techniques, and start the journey of bringing them there.

If you only started your involvement in bonsai now, I'm afraid it will likely take you a few years just to get there, particularly if you only have the chance to work of a few plants
I certainly took me half a decade, a few tens of plants (some now dead) and I'm really just a beginner in this...