Well you ARE able to do the same thing in Hexen (by using Vavoom), just not in KMOD/2 and in Scattered Evil as they use the jHexen engine. That means if you want to experiment with such things in a map, just download the latest Vavoom version (1.11.1) from www.vavoom-engine.com
and use the official Vavoom Hexen demo map as example on how to create the new things.
OTOH if you want to create maps for Scattered Evil, you'll have to stick to the old Hexen engine specs with the only extra of using MD2 models as building blocks (except for a couple of thatched roofs we've got only that wooden cube so if you need anything else you'll have to make the model yourself).
And here the numbered parts:
1) All houses that are small and have a full roof are dummies, but there are about a dozen buildings in the city you can enter. Go to http://www.korax-heritage.com/history/version_040/
and check out the city map, the numbered locations from 5 to 16 are all buildings you'll be able to enter (there is even a new building between 15 and 7 that you'll be able to enter that's not on the map).
2) Back in late 2000 / early 2001 I've been thinking for months to find a trick that looks relatively good, check out this shot
in the history to see what we're using (in the Scattered Evil section, if you look closely on shots where the Town Hall is present, you can see more such 3D objects at work).
3) You'll be able to add NPCs to the game, it's not yet clear how advanced they'll be. But simply putting an NPC is easy, somewhen around February we'll have a new hexen.wcf for WadAuthor that's got such items in the lists. The "ugly face" is Korax itself BTW [img]images/smiles/icon_smile.gif[/img] and the texts are put there by ACS AFAIK, which you can use already in plain old DOS Hexen.
About programming, Scattered Evil schedule is somewhat tight and it seems we've got the programmer capacity we need, but for later projects we definitely welcome any new programmers, so if you can hold out for a couple of months yet, cool. In them meantime you could study both the latest Vavoom source code and the Korax Mod sourcecode that's up on SourceForge (and KMOD2 code will follow in a couple of weeks, after the patch is released and it's clear that there won't be more patches).
I really don't want to limit someone's fantasy when making maps, but because of certain limitations of the Scattered Evil gameplay structure and code, there will be shops only in the main city itself (and there won't be any fights in the main city). There won't be any such limitations in The Serpent Power, but that TC might come out first in 2003.
Anyway, you're free to design maps the way you like them, but if I might put a request, for Scattered Evil we need maps with "uncivilized" themes, the more wilderness the better, since 95% of all non-combat non-puzzle interaction will be in the city only (shopping, talking to non-hostile NPCs, etc.).