12 down - dinosaurs (i know D is 500 in numerals and they are early creatures, not sure about rest)
D (500) in o (sphere) s (south) ur (ancient city) with "as" around it
19 across Tsar as form of rule and it's in the words although what part of the sentence is telling me to look in the words???
former ruler = tsar. "about" is the hint that it is in the previous words.
20 down Usurp - take by force fits and the word is found in Nauru surplus but why is 'goods' at the end??
No idea - maybe the setter thought it would be more obscure with the extra word.
1 down- thanks for the 'er' that's a good one to know. as for looks after another vehicle, i only know driver, chauffeur, valet. Says 'He' so thinking man's name in there somewhere. Thinking car name possible too that is also man's name with er in it...hmm
Hint: try putting the comma after the word "after", instead of "vehicle".