Alright, back with another quick update (and also a few small questions).

Both cuttings have developed roots by now:

I read that cuttings are good to plant as soon as they have developed several roots 2-4cm in length.

It seems that the first one is good to go, then? I'm going to leave the second one alone for a little while longer so its roots can grow a bit longer.

As has been said, on both cuttings the roots developed on the node right below the leaves.

Should I cut the stem right below the node above which the roots have formed? I also assume I should plant the roots as deep in the pot as possible, covering with soil until only a few cm below the leaves?

For clarification, here's my idea:

Cut at around the red line (node below lowest root formation)

Bury in soil until the blue line (a little below the leaves)

I guess I should leave the rest of the stem in the water and see if it maybe grows more roots?

I've heard this is possible even for cuttings without any leaves at all, so it seems worth a shot..

I am going to use the same soil I used for my mother plant, it is potting soil for acid-loving plants, mixed 50/50 with perlite too keep it loose, fluffy and properly draining.