Letting the first one dry is essential. Using MicroSol or MicroSet on the first decal will help it dry tight on the model surface. Don't use MicroSol or MicroSet on the second decal until it's in place and nearly dry and then apply a little carefully. You may move the first decal if there's too much solvent.
You say you're using homemade decals so be careful about the translucency of those. You may be able to "see" the first decal through the second. Test the translucency using a duplicate homemade decal before applying any decals. You might need to change your approach.
I worked on this last night, and had no problems whatsoever applying the second layer of decals withour clearcoating.
In this case, I was applying JT Graphics decals over my own, so translucency was not a problem. Basically, my home-printed decals are for panel shading, and then I'm using JT's for name, insignia, etc.
My decals dried for a full 24 hours before I applied the second layer.