I like to use straws for support, but I have never completed the support with the 1 long wooden dowel. I have 3 questions.
1. Is the long dowel really necessary?
2. Where do I get the long wooden dowels?
3. How/what do I clean the dowel with before using it?

1) no
2) you buy them at Michael's; any lumber store or hobby shop.
3) Never have cleaned them. Probably not the best idea but .....

If I'm assembling on site I don't ordinarily dowel, but if I'm transporting a stacked cake then I do dowel. I just sharpen the end going in first in the electric pencil sharpener to help it get through the cake cardboards more easily.

I buy the dowels at Hobby Lobby in the art/craft department or at Home Depot.

When I have to transport a cake I like the extra security. I often take my cakes to family 4 - 5 hours away. It is easy to do.

1. I use the long dowel when I'm super nervous about the client, summertime or just really want to deliver a biggie all put together.

2. Try to search donut turning sticks. I have a supply store here in California and my distributor will give me donut turning sticks from time to time. They are food save, plenty long and already have a rounded point on the end so you just sharpen a bit more and good to go. I bet you can search the net and find them.

Hope this helps ya.

If your cake is more than 3 tiers especially if it needs to be transported stacked, then you would be wise to use a dowel for support. If you are stacking on site, it may not be necessary but would be a good idea if the cake is expected to be on display for a while (for a few hours like at a wedding).

Even for a 3 tier cake, if it's to be transported stacked, you should use a dowel. They are relatively inexpensive so worth using especially if it avoids a disaster.

You can clean them with regular dish soap & warm water but I would let it dry well before using. I've heard some people use extract or an alcohol like vodka to wipe down the dowel but have never done this myself.

HTH.