As a clarinetist (out of practice, but nonetheless still a clarinetist) I can say that this is a very easy piece. Breathing and phrasing go together, so any competent player would be able to insert breaths where appropriate. You do have to understand, though, that this would come at the expense of some quarter notes being played as eighths, some whole notes as dotted halves, etc. This is just part of playing a wind instrument and there is no need to stress over it. Think of it like bowing. You would not write in explicit bowing for a violin piece except where it was essential to the musical idea.
Two other things: first, a clarinetist would immediately notice that you're not thinking about articulation. Every note is tongued - articulated the same way. That just isn't effective or characteristic on woodwinds in general in the style you're writing. At minimum you should think about the 16th notes. Slur two, tongue two? Slur three, tongue 1? Slur 8? It's all part of the way the instrument speaks and you shouldn't be ignoring it.
Second, if I were playing this piece I would be annoyed at being totally cut out of the Adagio and having to stand there and do nothing to do for 2+ minutes.