The Limits

There are 40,000 regions available, however in the Dream Editor, they are not visually numbered in sequence after the first 200. For instance, region 201 in the Dream Editor visually is represented as region 1, even though it really is 201.

You can use regions for indoors/outdoor DS and you can use regions for miscellaneous other reasons... but you may run into a problem with trying to use both methods at the same time. In some instances you can’t. When you can, you will likely be restricted to regions for outdoor use only. This is because indoor regions hide items and objects making it difficult to add interactive DS to them.