Try the Wilton website link for information on construction with dowels. This should help with your first question: http://www.wilton.com/wedding/makecake/building/dowelrod/dowel_tiered.cfm
Also, I checked in my copy of Wilton Weddings p. 113: 10 in or less diameter cake push seven (7) 1/4" dowels into the cake; the larger the cake and more numerous the upper tiers, the more dowels needed. Very large cakes need 1/2" dowels in the base tier.
Sorry, but I haven't a clue about your second question.
Good luck!!
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