I have finally gotten Greymont Bay to the point that I am ready to add spawners! I can't seem to find many tutorials about this step in the world creating process so I'm wondering if I am just overthinking it.

My main question is about freshwater designators - my rivers and mountain lake(s) are all fresh water. Or should be (haven't added them yet). Do I just need one designator per section or do the circles need to overlap everything so the water planes are completely encircled?

I plan on only using one rare spawner of each type (they should be rare, lol) but how many overall spawners are too many? If you take into account the different spawners from different EPs, there are a lot of spawners even if you just place a single one of each.

I read somewhere on MTS that the world event spawners are for future worlds so I won't be using those but what about nanites? Should they be limited to future worlds as well or can those be used in homeworlds?

Is it better/more desirable to only use spawners that "make sense" for the intended geographic location of the world or would it be better to include most of the spawners from the game?

I don't use the designators so I can't answer that question for sure. I would imagine that the ocean surrounding the world and any inlets/harbors should be salt water and any created ponds, fishing spots, etc. in the world should be fresh water. That's the logic I use when I place fishing spawners. As far as other spawners, I try to place most of them for each expansion pack I'm using. (I do include the nanite spawners if there is a bot building lot in the world.) I don't include Egypt, France, or China spawners unless it is a special lot like a Chinese garden or Egyptian exhibit as that doesn't seem appropriate to me. As far as placement, I try to make it logical - seeds near gardens, small birds near trees or in parks, snakes in rocky or wooded areas, gems or metals near mines, and so forth. (If you are including the crashed spaceship hull in your world, you need to include at least one spawner that generates the "mysterious fragments" to combine to make the key to open the spaceship door - digsite spawner; wasteland. Same for other "required" spawners - like the nanites - that are needed for certain activities.) I think it's a good idea to make the "rare" spawners rare. Hope this helps!