... I thought that the WAD would be enough to show you how to put a character into a level pack WAD and have it work. I guess I have to attempt to explain it.
Alright here is what you do. When you are sure you are finished with your levels, you open your Level WAD and select all the lumps and then press ctrl +c (this means you are going to copy something). Now you are going to need to open the character WAD. Paste the lumps after the character WAD stuff. After you did that, you are almost done, but you are going to want to move the MAINCFG of the level WAD to before the S_SKIN.
I think that is all you need to do. The reason why I say make sure you are done with the levels, is that when you open the WAD in SRB2 Doom Builder, it will capitalize every lump. If you run into problems, I think you should try to compare your WAD with the srb1 WAD and see if you might have misplaced a lump somewhere.