I think the most important barrier, at least in the beginning, will be the one in front of the stairs. I'm not sure there is a way to make that really safe without a gate.
When my son was little, we bought an little area rug that had a picture of roads on it. I'm sure you've seen it. He LOVED that rug-- he played with his cars and trucks for days on end. When he got tired of it, we simply picked it up and threw it out.
(Kind of like these http://kidcarpet.com/category.php?cI...FR895QodOVCNzA
but we got the $20 Babies R Us version.)