Kayzr, tiers are pretty simple. You need to put each cake on a cake card (thin board, usually 3mm) and stick them on with buttercream. I'm assuming the cakes aren't iced if it's going to be a skyscraper. Are they all the same size cakes?
The technique is the same even if they are iced and each tier is smaller than the last, I'd just use royal icing to stick each tier together.
You'll need 3 or 4 dowels per cake that you want to stack, depending on the size of the cake. Poke a dowel into the cake about an inch in from the edge, mark where the top of the cake is, take it out and cut the dowel to size. Cut as many as you need for the cake. Push each one in, about an inch from the edge so they are evenly spaced around the centre of the cake.
Put buttercream on top of the cake and position the next cake on top. Repeat with the dowels on each tier until it's the height you want. Obviously the top tier doesn't need dowels!
Hopefully that's as clear as mud!
For upright figures, I use sugarpaste mixed with CMC powder or Gum Tragacanth as it stiffens the paste and stops it sinking or flopping. My method is to make the body, let it harden, make the legs separately and poke a piece of raw spagetti into the top of each one. Let them dry too for at least a day then push the spagetti into the bottom of the body and secure with a dab of sugarglue.
HTH, Good luck .