For 17 I'm thinking it could be an anagram of TSAR followed by WEN ('new' reversed.) This gives an archaic word - connected with something that can be stubbly when it's been harvested.
Googled the characters to find the theme, about which I am totally ignorant. So I don’t understand the instruction about the path. However I have found a letter that occurs 8 times and so may have got the conclusion by luck. Is it 2 words of 4 letters?
The letter looks like that used in the thematic grid. Pretty sure the shortcut involves moving out the right side of the grid back into opposite left at one point so you end up with two four-letter words.
kobnut - I didn't bother too much with the route but looking at the letters before and after each of the thematic letters quickly resolved the endgame for me (I totally missed the craze for this sort of thing).