Not that I can offer much because it's been years... but I remember playing Emon sitting at the computer store while deals on the //e was being worked out. That started a lifetime of adventure game love. I hope you have some luck, sounds like fun. I would suggest looking for the source code for emon for at least the text part of the adventure because it was pretty solid and people were able to create their own adventures.
As for the graphics, I do like the mention of Penguin's Graphic Magician, as mentioned by the Devil's Compass, Transylvania was the next step in the evolution of the graphic adventure. I recently discovered what I think are my maps for that game.... crazy to see decades later. I think you'd do best working on the //e and //c using the double high-res graphics mode for the best images. This mode is much nicer, but does require the 64K extended column card.
I never had a mouse for the //e but I do remember seeing some.
You may just do best working on a PC/mac and then, if you can find a way to use, look into debabilizer (it's ancient but awesome mac tool) to convert your images to a format for the //. I don't remember if debab supports Apple ii, but since it handled almost everything and it was on the mac I'm pretty sure it did. Game devs used debab for a lot back in the day.