Hi, welcome to the forum.
The cheapest motion sensors (PIR) on Ebay have a normal working range of about 5 meters, maybe 10 meters on a cold day.
For good PIR motions sensors, a range of 10 meters is no problem. You find those in a good quality burglar alarm systems.
[EDIT] After reading the next reply of DVDdoug, I think it is about wire range, not PIR detection range.
Dimmable warm-white LEDs are very friendly, also to animals.
When you want to go nuts with a birthday or at Christmas, you could use one of the led strips from Adafruit : Digital RGB LED Weatherproof Strip - LPD8806 32 LED : ID 306 : $149.75 : Adafruit Industries, Unique & fun DIY electronics and kits
They have a few different kind of led strips, you need read the description of them to see which one is best for you.
When you have not made a project with Arduino yet, the Arduino Uno board is the easiest board to start with.