Thanks to all who gave this a go and for your feedback, much appreciated! Seems like most have finished, so just to wrap things up, here are the answers…
1. Leading characters in the top tier… (6) QWERTY
2. …on which Spooner plays in B major? (8) KEYBOARD
3. Snowmen merit a merry face (5,3,5) TIMES NEW ROMAN
4. As seen in “cow, causeway, and butterfly” (6,5) OXFORD COMMA
5. Compositor interference, like another here (8,7) PRINTERS DEVILRY (see 13)
6. Section of train ticket takes you to the next line (8,6) CARRIAGE RETURN
7. Assistant allowed speed to cut into printer’s material… (8) PAMPHLET
8. …in Russian. On editing, amazed it’s not English! (8) SAMIZDAT
9. 6 and 10 get tangled vine-leaves by design (8) VIGNETTE
10. Phonetic change the typist might use (5,3) SHIFT KEY
11. Nice day to signal second half review? (7) JOURNAL
12. Some printer’s material requires covering up (5) QUIRE
13. Colter created the character name
Den de Av’our (5) INDEX
[Un-devilled: Col
in Dexter created the character named Endeavour]
14. Printer’s material predicament (5,3) PAPER JAM
15. The key to Milliways? (5,3) SPACE BAR
16. Arsenal play amazing endgame! (8) MAGAZINE