If you mostly just wanna fiddle around a bit you should be fine without anything extra
You would most likely be interested in the 3D objects from the 2001 APCD (a lot of buildings), you can look up Lez' video about Library Merge for how to add them to your APCD, or much easier: simply download a full APCD with them already added at
viewtopic.php?f=16&t=348 and use that APCD instead.
I highly recommend checking out Lez' first 2 videos where he talks about how to set up and navigate APCD the most comfortable way, there were some really game-changing tips there that I was completely unaware of until I watched it, like panning with middle mouse button for example. Video 3 would probably also be useful in understanding the basics of how courses and APCD function. Can watch them at x2 speed to skim it over at least. Of course, his other 62 videos are useful as well...
Most importantly, if starting a course yourself, dont tick the "Allow non-regulation fairways" aka box of death!
If you plan on building 3D clubhouses, consider getting the 3D clone tool (it is not needed but highly useful if getting advanced) but it can be added to your APCD later on, and its probably better to focus on learning the basics of 3D first.
Otherwise its mostly about 2D object and texture addons, but they can be added anytime later.
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