Numbering pieces in a large score

You can combine these pieces in a single score, and separate each piece from the next with a Section break:
Handbook: https://musescore.org/en/handbook/4/using-sections-multiple-movements-o…

You can use a Rehearsal Mark at the start of each piece, incrementing the number of the Rehearsal Mark at each new section. Ctrl+M to create a rehearsal mark, then type the next sequential number in the outlined box.
Handbook: https://musescore.org/en/handbook/4/rehearsal-marks

Then you can navigate to each piece using the usual Find box for a numerical rehearsal mark:
Handbook: https://musescore.org/en/handbook/4/navigating-your-score#find