your instinct about using the forum id? absolutely correct.

basically what you're doing is, well.

<div class="boardlayouts-#"><div class="wideboardlayout">(board layout goes here)</div>
<div class="smallboardlayout">(board layout goes here)</div></div>
in the forum layout html template

then in the css, you're doing
.wideboardlayout, .smallboardlayout { display: none; }
.boardlayout-1 .wideboardlayout { display: block; }
.boardlayout-2 .smallboardlayout { display: block; }

that's it, that's the strat.

(or, y'know, there's the threads here and here that have better + more detailed instructions on how to do it, since uh. you are not the only one to ask that question l-lmfao-)

yes, it does.

basically, you're dumping every single possible board layout into the html template and then using a class that changes based on the forum id to specify which layout version is to be displayed for each board. the only real exception to that is that redirects use a different html template, so imo you can pull out a redirect-specific template from the general board list and stick it into that one only, but that's really only useful for a couple of boards, if that, so it's not much help to you.

(that's actually why i generally recommend trying to minimize the number of different layouts by styling as much of it with the css as possible - because ho boy it's not gonna be fun trying to load 40+ individual board layouts for each one of the 20+ boards that are on the index page tbeh.)