It's so natural that I can go between either comic/manga direction and not even notice.

I wonder if my brain would be confused by a manga going L-R?

Its actually my default now so when I read something "normal" I sometimes get confused.

What's nice is the webtoon format skips it all since it's just "read down"

Glad I wasn't the only one

Fun fact, it used to be right to left (1 letter each and line break in vertical writing, then right to left columns) before they adapted left to right western writings.

They're mostly gone by now but still some old places keep the order. For example, trad confectionary place named とらや toraya have their shop curtan reads inverse やらと yarato)

It is pronounced agnam.

Easy, you just guess the wrong pannel first every time, and then find out when the next page gives you the context.

Have the same question, but hazarding a guess - the rule of thumb would be using the bottom of the cells as guide?

I really am new to manga, but what I have noticed so far is that there are subtle flow queues in the art itself. For example, there might be a very thin line between those three cell and a thicker border between them and the larger cell to the left.

You tend to finish the right to left line to the end of the page before moving down any. So if 2 panels are in the same "line" like 2 and 3 are, then you finish out that line before moving down. In a case where one panel is larger and spans multiple lines it'll generally be laid out to belong to it's lowest line if it's on the left side of the page, or the highest line on the right side of the page. So since 12 covers both the line with 9, and the one with 10 and 11 on it you'll generally read it as belonging to that lower line and it'll be 12.

What are the benefits of a language being written to the right?

Neither is better or worse than the other, each works how it needs to for its language.

Japanese was written vertically, so characters are ordered from top to bottom while it is the lines which are separated from left to right. The slow leftward advancement allows a person writing on a scroll to write with their right hand while unrolling the scroll gradually with their left. In modern times you can write Japanese horizontally, but in that case you usually write from left to right. Characters written horizontally from right to left is only done in exceptional cases.

I don't know if there is an advantage or disadvantage. There are other writing directions as well. Like boustrophedon, which starts in one direction, and then when you get to the end of the line the next line goes the other direction. This sounds like a better way to write to me!

Egyptian hieroglyphs can be written either RTL or LTR, you tell because the animals and humans in the script face the beginning of the line.

Basically the priority is to make as many unbroken right to left lines across the whole page as possible. You don't generally move down unless you've reached the leftmost edge of the page. Notice how here if I draw lines across the panels to show the path my eyes take and read 12 before 10-11 my reading line is going to run back into the line I made already? So you read 9 and go to the next line, considering 12 to be part of that lower line so that your reading lines don't intersect.