Several pieces of advice:
- Go with frosted white bulbs for the General Illumination. Non-frosted bulbs will be too harsh if visible to the eye (that is, not behind an insert)
- Also for the GI, whether you go cool white or warm white is personal preference, but cool white light tends to accent playfield colors like blue and purple, while warm white highlights oranges and reds.
- Color-match inserts. If an insert is blue, put a blue LED in it, etc.
- Check out the sockets under your playfield. For any inserts where the socket is sideways, consider getting flex-head LED's so you can aim the light upwards. LEDs are a little more unidirectional than incandescents, so when one is at a 90 degree angle to the insert, the insert might not be lit well without a flex head.
- All of the vendors TheDudeAbides mentioned are great. You don't want to go direct to China for this type of thing - these vendors have already done a ton of product iterations and trial and error with them to get their products just right for Pinball.
- Don't get chincy with the quantity. Count how many you need of each color and style, but order a bunch of extras in several different variations. You may end up not liking how a certain type of bulb looks, and it's better to spend the 75 cents on a spare than to make a whole new order with shipping, etc.