The number of files depend on the asset.
Lets say you wanted a particular placeable:
You would need the MDL, a PWK if it has one, and as many TGA and/or DDS files (textures) as it uses. And then after that if any of those textures have a special TXI file you would want to get that too.
You would also need to add a line to a "placeables.2da" (I assume this is the one in project Q - in whihc case you extract that from Q, make edits and put it in a new HAK so as not to change your copy of Q).
Usually however 1 placeable is 1 MDL, 1 PWK, 1 DDS, 1 TGA, and one line on the placeables.2da.
This is a multi step process in which you will learn how to extract resources from HAKs, read and write 2DAs, find texture names in a MDL file, and then combine all the new stuff into a HAK.
I started writing the steps below, but then realized that its better that you just get started, rather than get hung up on the exact process.
Here's a very rough sketchy and incoplete step by step
How do you go about doing all of this?
Step 1: load up a module which uses CEP and has all of its blueprints (to make it easy on you).
Step 2: call up the "properties" of the placeable that you want. Look at its "Appearance" property. This is a string value.
Step 3: open up CEP's placeables.2da (you previously extracted it from the CEP HAKs) in a TLK editor or if you are an menche use Notepad++ (ubermenche's use vi from commandline). Me I just use Tlkedit.
Step 4: search for the exact appearance name in the placeables.2da (hopefully CEP did not obfuscate these values with TLK entries because I don't feel like adding that step to this) (copy this entire row for later use into a separate text file)
Step 5: On the same row as the matching appearance name, look at the name of the MDL.
Step 6: Find the MDL and PWK with the MDL name in the CEP HAKs and extract (if the PWK is nowhere to be found don't sweat it)
Step 6: open up the MDL in Notepadd++ or any text editor and search for BITMAP, and TEXTURE and write down all the BITMAP/TEXTURE names (someone probably has a script for this. (I did once but don't know where i put it))
Step 7: Get all of the textures from the CEP HAKs
Step 8: Recombine this stuff in a HAK
Step 9: put the copied placeable line at the very end of your placeables.2da and put that in the new HAK too
Edit ....
and lastly I want to caution you again from caring about art assets. Build the game content first using default assets. Then worry about going back and providing the shiny art assets. You can spend all your time just curating art assets. I've done far more than my fair share and wrote command line tools to manage this stuff at one point (on linux) because I was dealing with ... far more assets than could be moved about by hand, renaming, changing textures, and so on. And then I stepped back and realized that you can never have enough art assets. You always want more and more and more.
My philosophy became use what you've got and make a list of what you absolutely must have. Put that list aside. And then maybe later import the stuff.
For you I again recommend just using Project Q or CEP as they are and try to use everything thats in them. Just build with something that is plug and play. If someone gives you a top hak for merging, great. But don't wait for it. Move forward with teh actual game play.
