I want to know before I go on and make a half assed attempt at a 128 resolution pakset made entirely from scratch.
Yes, that does sound like a certain other project I contributed a few sprites and other misc files towards, for a certain other highly moddable game (http://www.bay12forums.com/smf/index.php?topic=160947.0).
I'll use pak128 as a base, and strip all non-essential stuff in the process. UI and other code will be considered essential because I don't even know what will happen when I screw with them and I don't want to find out.
After all, I'd rather ask a stupid question instead of spending hours checking for the answer online.
pak32.comic has more or less the bare minimum. More than one house of RES and COM is not strictly needed, but will given strange cities otherwise.
simutrans-germany.com/wiki/wiki/en_creatingPaksets (https://simutrans-germany.com/wiki/wiki/en_creatingPaksets)
I can't say to what extent this is still true.
A basis for a set can be found here. But that's already 10 years old. I can't say whether it will still work that way.
https://sourceforge.net/p/simutrans/code/HEAD/tree/pak96.hh/ (https://sourceforge.net/p/simutrans/code/HEAD/tree/pak96.hh/)
EDIT
I testet
you must rename ground.Outside_.pak to ground.Outside.pak for latest simutrans
and add pak96.hh/config/simuconf.tab
# how height is a tile in z-direction (default 16, TTD 8)
# THIS WILL BE ONLY USED, WHEN THIS FILE IS IN THE pakxyz/config!
tile_height = 8