It depends on what you mean by specific things, I belive the dungeon masters guide has some guidelines on making your own world. But the point of many of the rules is to be (mostly) setting neutral, so you just take the rules and put them in whatever setting you want to describe.
Pets? Quite a few spellcasters get familiars, which are small animals that give you small bonuses and are basically pets. You can also take feats to make them better/bigger. Quite a few classes get animal companions as well, which are bigger animals that normally scale up over time and are useful in combat.
Making your own races is pretty easy, I don't personally normally do it since there are so many races spread thoughout the world of splat books. But it is normally pretty easy. At it's core in 3.5 all you really need is +2 to one stat, -2 to another stat, and then add some bonuses to some other things.
On the map thing, I would suggest you don't do that (with a exception). Making a whole setting with all the details is a awful lot of work, like, even published settings normally don't have detailed maps in the main book about them for all the major cities. And the often that work won't even go to use as your players largely ignore or bypass the stuff you've made. I guess it depends on what type of game you are planning on running. A heavily on rails game could use more planning, but with a game that is more free form I find it's not worth planning more then a session or two ahead.
The exception to that is if are ether making it for fun, if you enjoy mapmaking and lore writing and you don't mind if it's never used.
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Topic: [MILK] There were 12 eggs here what did you do with them? (Happy thread?!) (Read 16263699 times)