I've had a similar idea for a few years (I was an electrical engineering student), and it's really hard to make it in hardware. You will put a lot of effort, and the product may not work at all! This spring I was finally able to make a lucid dreaming android app, using a lot of the features I thought of over the years.. You can find the source code (java) here: android-lucid-dreaming-app - Using Android phones to induce lucid dreaming - Google Project Hosting . It does quite a lot of things that you mentioned, although the success rates have been pretty disappointing.

-customizeable alarm tones
-autosnooze
-custom timers
-ability to mark up dreams
-Digital clock in any color!

What it is missing is a solid method of detecting if the user is dreaming or not. Without it, TOO much effort is needed to estimate when to play reminders.