I put them in my Chevy truck. To answer you questions.

You should use bulbs that emit the color of the lens.
The standard ones are not as bright as the regular bulbs, unless you go with the 3 watt design(very expensive).
You need to change out the flasher.

Here is the site I bought from.

http://www.superbrightleds.com/led_prods.htm

It has answers to all the questions you may have additionally.

Instead of going LED, I removed the tail lamp lenses and put a reflective tape on the inside of the housing to help direct light out. Seemed to improve the brighness a little bit.

Consider carefully, the install in my truck, tail/brake and front marker/turnsignals with new flasher ran about 100 bucks for all parts.