Could anyone advise me on how best I can get started with creating addons? There are just so many things I'd love to see in Simutrans and I figured creating them myself would be loads better than making requests. Thanks!
The best starting place is downloading examples from sourceforge, where pak64, pak128 and some other paks can be found. There you will get basic examples for drawing.
This is the most difficult part. Generating dat file to merge them with makeobj is very easy and really depends on what kind of object you are makeing.