Hi Tom, welcome to the forums, and congrats on your purchase. :)
If you click on Lenny's profile in the link below, you can find a lot of good mods to get started with, including some interior mods.
Clive also made a really good guide on how to fit footwell lighting if your car doesn't already have it. (If it does, just pop bulbs in the sockets.)
Replacing the interior bulb with an LED is very easy, you just have to pull out the unit by prying it at the front with a flat screwdriver, more details here: