Hi WebCPCP,
I don't have time today to write out a full instruction list for you, but for the "previous" button, you can make one using the Button Free Field Plugin.
In the field settings, make it link to editing your content, and then
click the "+" and you can select specifically which stage you want the
button to link to. So, on each stage you need to add one of these
buttons and get it to link back to the previous stage.
Regarding
showing a field on all stages, I don't think it's possible. You need to
duplicate it and add it to each stage you want it to appear on.