We probably need more information here. Did you get the newest version (see link below)? Mac vs Windows? What error?

https://indesignsecrets.com/placing-all-the-pages-of-a-pdf-inside-indesign.php

Did you turn on the Balance Columns checkbox in Object > Text Frame Options?

Multiple indexes is not easy in InDesign. Here’s one article from a long time ago:
https://indesignsecrets.com/creating-multiple-indexes-in-indesign.php

Nope. That requires two different paragraph styles. Someday I hope we’ll get that feature!

I just added this to Uservoice… please vote for it!
https://indesign.uservoice.com/forums/601021-adobe-indesign-feature-requests/suggestions/39166843-remove-first-line-indent-after-a-heading

Ah! Interesting. I’ve never seen a template for something like that. One idea is to create the page normally, and then select everything and rotate it to the angle you want.

I’m not sure what you mean by “diagonal grid.” Do you have examples you can share?

That script is awesome.
Another option is to put 2 graphic frames on a master page, and set them to object > Fitting > Frame Fitting Options to “Fit Proportionally”
Then you can go back to the document page. Choose File > Place, select the PDF, and turn on Show Import Options. Choose to import all the pages from the PDF. Now you just need to click on the first frame, then the second, then press command-shift-P (or ctrl-shift-P) to add a new page, and then click-click again, and keep repeating that. It’s monotonous, but it’ll only take about 5 minutes.