Can you use any Apple watch band on any Apple watch as long as the face size in the same?

If you go to the Watch site (on the menu bar above) and look at the different models you see that some models use a more integrated method of band attachment. Others use a bar for attachement that allows more flexibility in band use.

All bands use the same method of fixing so yes, just make sure its 38 or 42mm. However, not all band watch combinations look good.

The classic band has a loop at one end, but the loop in on the clip.

The only ones that are not compatible (and thats only because they are not available) are the edition bands. All bands have exacly the same connection. The integrated clip is just a metal loop in the standard connector.

all bands work all three lines with the right size. they just might not look good/match because the bands have little metal bits on the buckle.

All bands of the same size will work with any watch according to Apple.

I am hearing that the Sports Edition Watch is compatible with other wristbands, for example, the stainless steel bands or ones with a buckle fastener? is this the case? Can anyone confirm?

Yes they fit.

If they look good is another question.

Apple confirmed any band will work with any watch of the same size. I ordered some different colored Spigen Watch Bands for $15 a piece. The Apple ones are way too expensive!

As best I can find, Spigen does not make watch bands for Apple Watch, only cases. I have gone through Amazon and Spigen's web site. Amazon does have several other sellers of bands, but customer reviews for most are very poor.