You are talking about page 18 "lab supply" circuit? I presume it can work well.
Regarding inverting LM2576 operation, I've often used this configuration. -1.2 V output sounds like you have LM2576-ADJ version with 1.2 V reference voltage. You can add a reference voltage divider to get higher negative output. I don't know how the question is related to 0 to 5 V regulation problem?
What's your specification, just 0 to 5 V or also current regulation? How much output current?