Creatures Caves

Hey there, nice to see a new face around! I'll try my best to answer these questions. However, take some of these answers with a grain of salt, as I never played C1 or C2 myself, only C3 and DS.

1. If you are already on steam, that should be a good bet for you to use. Those are the versions that have been put out the most recently, and should require the least fiddling around to run. GoG.com also offers Exodus (= C3+DS) and Albian Years, however even those require some extra handiwork before they function on a brand new OS.
If for some reason you are using a retro system, like, say, Windows XP for example, I'd say the GoG version is probably preferable, though.

1a. I mean, "modding" these games works slightly differently than for other games. The games have their own script languages and file formats that you can use to make custom objects and drop them in. The steam version should allow for that, as you had to pretty much rework the whole engine to get rid of it. However, just keep in mind that this is a manual process, where you download and install the files from a website of choice such as our local download section or Eem Foo's Archive. You will not be able to swap out e.g. the core engine parts or use the steam workshop, as with e.g. Skyrim or Fallout.

2. I have to admit that our community is somewhat small these days. CCaves here is pretty much the main hub forum-wise. There's always the IRC Room if you want some live chat (irc.creatureschat.com #creatures if you have a dedicated client) and there's a couple Discords around.
As for a general knowledge base, we have our own wiki. Please refrain from using the one provided by Wikia/Fandom, as the majority of the community renounced that site over some legal disputes.

3. The creatures in C3/DS are a lot more independent. With the right setup, you can leave them to their own devices for many generations. C1 creatures need to be nannied a lot more. However, that also means that you form a closer bond each one. Not sure where C2 creatures stand.
There are also some minor differences. C3/DS has a basic physics engine for objects for example. And there are some quirks in the vocabulary, such as the word "eat" not existing in C1. Creatures have to "push" their food to consume it.
Overall you're well served with any PC version of the games, though. It's usually the console ports that are a tad, uhm, anemic.
As for "adding C1 to C3/DS" you are thinking of the C1toDS project. The gist of it is that you can add custom rooms to C3/DS and someone decided to make huuuuge ones that recreate the entire C1. It's not a perfect 1:1 recreation due to differences in the engine and such, but it's pretty good.

3a. The original purpose of DS was to add online functions to C3. That way you could swap out creatures with other people right there in the game. You could also have a simple chat running from within the game. DS also has a slightly updated engine that fixes a few (though by far not all) quirks of the original C3. DS itself is playable on it's own, so it doubled as a free demo as well.
Even though the servers are down, you can still profit from the newer engine and some of the objects that DS comes with, like the hoverdoc, so there is little reason not to play docked, unless you have an older PC that struggles under the entirety of the C3 world.
As for custom server replacements/alternatives, Albian Warp is probably the most developed solution we currently have.