Yes, rebuilding the prefs is to hold down everything when restarting. If you don’t see a dialog box saying “Rebuild preferences?” then it didn’t work.

If that still doesn’t work, and if you’re on FB, you might try asking our larger community there: https://facebook.com/groups/indesignsecrets

I don’t think InDesign can do this automatically.
If would be easy to use Find/Change (GREP) to add the parentheses. Search for .+ and replace with ($0) (and restrict the search to just the one paragraph style)

You can add text at the beginning of the paragraph… kind of… with this trick:
https://indesignsecrets.com/add-custom-text-at-the-beginning-of-each-line.php

I think this works:
.+?[.!?]\K(.+?)$

You can get that transparency icon in the Pages panel if you want it… I think it’s an option in Panel Options (in the pages panel menu)

Yes, drop shadows are one of the forms of transparency. Here’s more on the topic:
https://creativepro.com/my-grayscale-images-and-colors-changed-suddenly.php

What resolution do you need? It is a digital book, right? So you probably do not need more than 150 ppi, unless you expect people to zoom in a lot.

One way to figure out resolution vs. pixel dimensions is to go to Photoshop and open the New Document dialog box (cmd-N). Then set the measurements to pixels and type in 1152 and 1536 for width and height, and set the resolution to 72. Now change the measurements in the dialog box to Inches, and you can see that it’s a 16 x 21.3 inch document. Big!

Now, if you want that to be 150 ppi, change the resolution to 150 and then change the measurements back to pixels. The width and height update to 2400 x 3200 px. That is the pixel dimensions for the same size document, but at 150 ppi.