Let me make sure I understand...Before laying the sand, box the area in with 2x4's, then notch the ends of a 2x4 that will span the width of the box so that I can run it across the boxed area?
Should I use sand or that sand based grout?
NO GROUT BASED ANYTHING. Use sand. You want the flexibility the sand will offer. If the sand isn't a little damp then spray it a little to make it so.
Remember you are going to excavate for the gravel and the sand and the pavers. You want the gravel and sand below grade and contained by the edges of the dig. If you don't plan on using paver edging then excavate for the paver thickness also.
Then you'll have to do-the-math to determine how to notch the screed so that it hangs on the forms and creates the proper depth for the surface of the finished sand.
Screed the sand, tamp the sand, add any needed sand, screed the sand, tamp the sand, add more sand (if necessary), screed the sand, tamp the sand....
At some point your sand will be flat and smooth and you should be able to walk on it without too much disruption. At that point you are ready to place the pavers.
These things are really simple and actually a lot of fun. Don't forget your gloves.