NOTATIO

The first example looks better to me, but you should adjust the staccato dots so that they are parallell to the gliss. line.

From the G. Schirmer Manual of Style and Usage (Second edition):

"We do not use dashed ties for tremolandi, trills or artificial harmonics".

IMO totally unnecessary and just adds clutter.

If it is imdeed C-natural, than the auxilliary note would better be spelled as a D-flat. Otherwise you definitely need the natural. To be extra clear, the bottom C should also have a natural.

Depending on the tempo, it might be clearer to tie the two C-naturals.

Have you tried using a multi-arced slur?

Boosey (or rather, Philip Rothman) is using it to engrave their new Copland critical editions among other projects. Peer uses it for some of their Ives critical editions (at least for the songs). Sibelius used to be my first choice app until Dorico version 3 appeared. I don't know that it is any wor...

There is a way to get the prefatory clef.

IIRC you have to move the "+1 staff" signpost back an eighth or so, then you enter an explicit clef.

It's very easy.

Highlight the three measures, select "ossia above" from the context menu, and Bob's your uncle.

That is the version i ended up with when I upgraded to Dorico 5.

Very close to 10 X 13, which is common in the US (like a Kalmus or Lucks orchestral part).