Have you ever made a string quilt? If so, and you liked the process, then 1.5-2.25 for strings is a good size. Having the strings ironed , stored neatly, and ready to go will be great.
If you haven’t made one, try a baby quilt or table runner. You may find your answer about whether you like that kind. If not, you wouldn’t want a bunch of strings that won’t get used.
2.5 is great for bindings and many popular patchwork patterns. The key is finding out whether it’s your style. I have had 1500 2.5’s for many years that I got in a swap. Found it was more fun to collect than to use. So not gonna waste time cutting or collecting more. I like big pieces .