Extra Practice is at the same level (or easier) as the workbook. We used it sometimes, but then in later years I got the tests and just used some of those for extra practice if it was needed.
We used IP and CWP regularly. They're excellent. I'd let ds get stuck on some problems and return to them day after day after day (work for a bit, get stuck, put it away for the day, do other math that day, get it back out the next day and try again). I loved him getting the experience of struggle.
Process Skills used to be iExcel. It's designed to show how to approach some problem types with the bar models. I like it and found it helpful for some CWP/IP work.
For summer review, I might go with IP as first priority, then see what other supplements you may find useful to add in.
We do a good bit of math :)