Yes to most of your questions. You're on the right track in your thinking. The answer ranges between all mics in a single horizontal line, to the center mic being moved well forward of the omnis (with compensating delay applied to it). Usually having the center just slightly but not overly far out in front (without any compensating delay) works well for both practical and acoustical reasons, which I'll try to outline in more detail later.
The good news is there is a lot of leeway without screwing things up. Much more than there is with simple 2-channel stereo configurations.
Edit-
After posting a bunch of stuff explaining why later in the thread, here's a short synopses of my practical take away-
For section recording using only a pair of omnis alone, I want an spacing of about 3'. Less isn't as good in terms of imaging, ambiance, bass, and openness. More spacing might work but risks a hole-in-the middle.
If using a center mic I want an omnis spacing of 3' or more. Less isn't as good in terms of imaging, ambiance, bass, and openness, and risks imaging and comb-filtering complications more than just a pair of omnis alone. It could be advantageous for other reasons though. More spacing between omnis can be beneficial and is less problematic because the center mic fills the hole in the middle, but I still wouldn't go crazy wide or the center is becomes separate and "spotlighted".
If the omnis can't be spaced far enough apart, it can help to move the center mic well far forward (like 6' or so) and delay it to compensate for that distance, but that's not often practical. Alternatively one could move the center mic it straight up or straight down, without requiring any delay, but that might not be very practical either. Either approach gets the three mics far enough apart to minimize problems of having them too close to each other. You don't want the three mics too close together.
By using a coincident center pair in the center instead of a single mic, I optimize things and get the best of envelopment and imaging at the same time. Like a single center mic, I ideally want an omni spacing of 3' or more for the same reasons. Yet because I can then adjust the image width of the center coincident pair, even wider spacings between omnis no longer present a problem. I can go double-wide or even more with the omnis without potential problems, giving me a wide diffuse ambience which stays out of the way of the sharp directional imaging stuff in the center provided by the coincident pair. I also gain control over image blend between the center and sides of the playback image by varying the width from the coincident stereo pair afterwards.