What is the size of the CREDIT Lump?

It is a graphic which is 320x200 in size (like TITLEPIC).

To give credit to whoever had any influence on your pwad you have several options:

1. A 320x200 graphic lump CREDIT.

Take for example the pwad DMP2012 which has a graphic CREDIT. 

2. A standard template (item 6), any size.

When you download DMP2012 it is accompanied by a text file, to let users know the specifics of the pwad and who is to be credited if that applies.

3. A text lump CREDIT, any size.

But, instead of supplying a separate text file, one could create a text lump CREDIT with Slade3 to insert the contents of the template as text.

4. Do what was done in Brit11, any size.

Create a special map with custom textures to mention who is to be credited for whatever.

6. If you make a pwad for say GZDoom then you could make a script to scroll credits as was done in The Refinery. To see the credits roll by puke script 81.

If you create a text lump, CREDITS would be a better name than CREDIT since the latter clashes with the graphic lump name and some ports might try to interpret your text lump as a graphic in some circumstances.