Even better is using paper cards - one idea per card; can arrange in front of you or pin onto a board. Like https://www.lesswrong.com/posts/NfdHG6oHBJ8Qxc26s/the-zettelkasten-method-1#Zettelkasten__Part_2__Further_Advice (ignore Zettelkasten part - look at the image)

(setq org-agenda-files (list "~/org/)) has a missing closing ".

Also, check out https://archive.org/details/gnuplotinactionu0000jane (Gnuplot in action : understanding data with graphs)

If opening a file is a problem, you can create temporary buffer and then use insert-file-contents + search + erase-buffer.

You can simply loop over all the org files, open one by one, and search within each file individually using (while (re-seacrch-forward …) …).