Courtesy Systems: How to format them

I am editing and engraving a Baroque score that uses tenor, alto, and soprano clefs for the tenor, alto, and soprano parts. However, in editing it, I want to use modern notation and have the three parts in treble clef, and I would prefer to have a courtesy system showing the original clef and, if possible, the original key signature. I am wondering if anyone has any directive or advice?

I am using the Neue Bach-Ausgabe as a close stylistic guide:

Here, the clefs, and differences in transposition for the brass, are indicated, and not for the violins, etc. Additionally, the courtesy system is approximately 80% the size of the actual system. Is there a way to accomplish this, or to accomplish something looking similar?

The closest thing I could figure out,

is creating a horizontal frame between the first and second measures and setting it to zero. This creates an extra bracket on the second (or actual first) measure. For the uniquely-marked key signature, I added invisible notes and moved their (visible) accidentals to align the way I wanted them. However, I am unable for whatever reason to hide the bracket for this first courtesy measure. Pressing "V" does not do anything, and deleting it obviously deletes the bracket I want to keep, as well. Also not as necessary but definitely preferable would be to use an actual custom key signature instead of odd accidentals (is this possible?), have a smaller staff size for this measure (how to do!), and, when necessary, only have a courtesy measure in, for example, the soprano line but not the bass line, as in the Neue Bach-Ausgabe example.

Advice or suggestions for any one of these questions would be greatly appreciated. Thank you!