Feeding sourdough rye flour, etc.

mizrachi, so many questions!  Let me tackle them in order:

I've been feeding my newly acquired Danish Rye starter equal parts rye flour and water and it's doubling if not tripling in volume big time. Since I just started reviving this dried starter I figured I'd give it about a week of twice daily feeding in order to develop and activate the culture, but with this much volume I'm forced to dump most of it out so that it doesn't explode out of its container. Is this the right thing to do? Or should I adjust the feeding quantities.  You don't mention your feeding ratios.  You should be able to feed it at a 1:1:1 or 1:2:2 ratio (starter:water:flour) and do fine.  Your container should have enough room for your starter to quadruple in size.  You don't have to keep much starter, so if it is growing well, try reducing the amount of starter you keep and using the ratios described above.  For example, you might keep 15 grams of starter and feed with 15-30 grams each of water and flour.  You won't have as much waste that way.  It should be quite active in two weeks.  Personally, I'd bake with it a lot sooner, especially since you began with a mature dried starter.

I read somewhere that rye flour really activates a culture and since it's a rye starter I thought feeding it rye flour would be the right approach. Does this also make sense?  What you feed your starter depends on what kind of starter you want to use.  Just as you can vary the hydration of a starter (see below), you can change the type of starter by feeding it a different type or blend of flour.  If you want a rye starter, keep feeding it rye flour.

Lastly, if I'm aiming to achieve a specific hydration of a sourdough starter that may be different than its current hydration, do I simply dump most of it, and then begin feeding it at its new hydration levels? How many feedings at the new ratios would accomplish a change in hydration levels? Do bakers constantly change the hydration levels of their starters to fit specific recipes?  I think what most people do is to keep a starter at their preferred hydration (100% seems to be popular and easy to maintain), and then take out a measure of starter to adjust it for specific recipes as needed.  Two to three feedings at the new hydration level should be enough to convert it, especially if you are feeding at a 1:2:2 ratio.  That way, you have a starter at the hydration you want for a specific recipe, but you keep your mother starter at whatever hydration you prefer, rather than changing it every time you need a different hydration.

Phyl