In general, I like to say “if it looks like a table, it probably should be a table.”
However, I know that many people make these kinds of tables as paragraphs (rows) and tabs (columns). For simple layouts, that’s easy enough.

But tables offer a number of features that are a pain with “tabular text, including alternating tints, graphic cells (in CC 2015), easy reordering of columns, and so on.

I see that you have an empty paragraph between each text paragraph. I suggest just setting the Rule Above to the paragraphs that have text, and then using Space Before to adjust the space between the paragraphs.

Making diagonal lines like this is not straightforward in InDesign. I used to use this method:
https://creativepro.com/diagonal-headings-in-indesign-tables.php
But I have a newer formula which I’ll write up as a blog post soon.

See this blog post for possible solutions: https://creativepro.com/when-indesign-ignores-your-leading-values.php

Pariah did a 5 or 6 part series of tabs and tab leaders, starting with this one: https://creativepro.com/tab-leaders-part-1-separating-columns-of-text-with-dots.php

You need to double-click master B to actually be viewing it. Just clicking it only selects it.

But instead you might want to set up Master B to be “based on” master A. That way everything on A would also be on B (though you could then remove some of the stuff on A if you didn’t want it).

Question 1: My guess is that you would need to choose Edit > Paste without Formatting instead of just pasting.

Question 2: Try moving the edges of the objects even 1 point away from the edge of the page. Did that fix it?

Great question. I don’t think there is a shortcut for that. Shift-Esc should do it, but it doesn’t with a text frame. Maybe someone could write a script to place the cursor inside the currently-selected text frame, and then you could assign a shortcut to it. Would you want all the text in the frame selected? Or just place the cursor at the beginning of the frame?