I found if you starch from the bottom side and press on the top side, it keeps the starch from collecting on your iron. I normally starch my fabrics using the dunk, squeeze thru a wringer and hang method. So the starch is on both sides but I have never had an issue with starch getting on my iron. If I have to spray more starch on the block I starch from the back side and then press. If you let the starch soak in before you press, that also will help with the buildup.
As to cleaning your iron of the buildup, I use Dritz's "Iron Off" in a tube found in the sewing dept of Walmart. I put some on an old rag and run my iron over the stuff. It may take a couple times depending on how much buildup you have but it works great for me. I haven't had to use it in some time now.
[