1 Sky

I don't want it to tile. How large should a sky be to stretch the entire map?

No skybox?

Make sure your skybox texture is 1024 units wide, and IIRC 384 tall. You'll have to do some offset adjustment regardless.

128 tall in Doom.

Apparently, 544 tall corresponds to the maximum in ZDoom (looking for as high and as low as allowed by the software renderer).

As for the width, if you use 1024 it will not repeat (true in any port). To have a 1024-wide sky in vanilla, you need to use four different patches that are 256-wide each. The earliest example of such a sky I've ever seen in Doom was trinity, back in the 20th century.

I meant 384, for what it's worth. AFAIK my old duel map with a 384-tall sky worked in PrBoom+

Thanks, I've got it working now. Another question: How do I change an image into the Doom Palette without having to perform color remaps? (ie, alternate software)

XWE does it automatically.

Sorry, let me clarify. I know that, but I'd like an alternate program that allows me to make changes otherwise not possible via color remap on XWE. Like, a photoshop program that is limited to that palette.

GrafX2 is worth investigating if you're working with 256 colour images.