that all sounds fine. I say stick with what you have for a while some months perhaps. When you get comfortable in the second octave you are beginning to get an embrouchure. An embrouchure is a lifetime thing. It also fades quickly if you don't practice.
Yes practising steady tones is good. There is also vibrato which is a wavering tone. The idea is to have control and deliver what you need. Practice playing softly, then gradually loudly - on the same note.
As far as fingering is concerned start with three notes of a simple scale, when the fingers find them automatically, then add another note, dropping one from the other end.
Notes beyond D lower register are harder to blow, esp at first. If they are near impossible, then you may have a leak somewhere (anywhere) on the horn. Make sure you don't try to fix this yourself as its a black art and can take years to get the touch.

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