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What to look for in beginner etudes for a second instrument?

[Stumbled upon this on meta. So I thought I'd attempt a trial by fire.]

I just got a shipment of necessary equipment for my new viola (shoulder rest, replacement rosin, decent bow), and I'd like a recommendation of beginner's repertoire. Beginner to the instrument, that is. I've studied guitar for 20 years.

I'm looking for something like Colección de estudios para guitarra by Dionisio Aguado, where the studies are short, focus on varied techniques, of progressive difficulty, and most of all musically interesting like Aguado (or Sor, but he's a little less accessible IMO) ... where you come back and play them again later just because they sound so marvelous.

Is there something like this for the viola? Or for violin or cello (I can read other clefs and transpose)?