Should textures be big or small?
What's the limit, if any at all?
Must they be kept in powers of two?
Should I keep one in my shoe?
Textures should be no bigger than your current desktop size (on lower spec machines), and I don't know the limit on higher spec vid cards.
Powers of 2 to keep compadible to all hardware (some geforce cards don't like oddball textures).
Your shoe is a great place for them.
I agree with the shoe, but textures MAY be bigger than your desktop. It's images that are limited this way.
Textures may be up to 2048^2 Pixels, but on some cards they are scaled down to 1024^2. Personally I would't use more than 1024.
A 2048^2 texture theoreticly eats 16 Megabytes VRam. A 1024 only 4 Megs and a 512 only 1 MB.
Their size should be power of two, where width and height may differ (eg: 512*128). If they are not, they will be upscaled internally to the next power of two size.
Also very thin / long textures may not display correctly with some older hw/driver stuff... keeping everything under 1:8 (height/width) should be quite safe.
Also, if the object which uses the texture only takes up a small region of the screen space - say 64x64 pixels then there is no point using a 1024x1024 texture for it!
I think that was the best first post ever.