I was a little concerned about the bulk for the elastic when using two layers of fleece but it came out just fine.
The assembly is quick and straightforward. If you try this pattern and something doesn't make sense I found this YouTube video that shows the assembly in detail that might help you with assembly.
When you get to the end you make an inside-out sandwich with the soles.
That non-slip fabric is totally necessary for me. I have no carpet in my home so not slipping on the laminate flooring is important.