To answer a few questions rather than recommend parts: each emitter has a maximum drive current. Modders are always pushing these limits are over-driving the emitters. You have to look at the thermal path from the emitter to the flashlight body and get a feel for how much heat your light can handle (i.e. can the pill & body handle an LED being driven hard and putting out a lot of heat?). The P60 is a great place to start (sorry gords!), but if you drive an XM-L hard in a P60 light you risk burning up the LED and/or driver. You can drive them hard, just don't leave it on high tail-standing on a table for a long time! Drivers also have different voltage requirements and you need different drivers for different purposes (i.e. a boost driver when using 1 or 2 AA, buck driver when using 2 or more Li-Ions, etc. . .). Drivers also have different modes with different levels of output. The Nanjg drivers are widely loved for their 5%-30%-100% output levels and the ability to not have blinkies.
Get familiar with the flashlight Wiki, especially emitter bins, and the tint chart references (thanks to user brted). Many users prefer neutral white tints, while cool whites are more commonly found in ready-to-use lights.
Understand the difference between thermal compound (grease) and thermal glue and don't mix them up. Thermal glue is a more permanent attachment method. Fujik makes both (see on FastTech). Fujik brand is ok, Arctic Silver and other brands are better, but not necessary for basic builds.
My suggestion? Build a P60 with a Solarforce host (watch out - most are forward clickies on the Solarforces!) or Ultrafire 504b or this one, use an XP-G2 neutral white (if you can find one), and drive it around 2.1A to 2.4A using one of the Nanjg 105c drivers set to 3 mode (Hi-Med-Lo). Oh, and don't forget to get some copper foil to wrap that P60 module in to fit it into the host tighter for better heat transfer (I've bought from this seller).
Good luck and happy modding!
-Garry