I just did some reading about those Elac speakers you bought and everything I read says they are a huge bang for buck, beating many speakers that are twice the price or more, not even including your amazing deal on them. Congrats buddy! I'm sure they'll be amazing with your new Denon!
I built my own speaker stands, but I'm sure they're not as rock solid as some nice professionally made stands. I made sure to measure the height from the floor to where my ears are when sitting on my couch, and measured on the speaker itself from bottom up to tweeter to make sure I built them so that the tweeters were at my ear height. Actually just an inch or two above. If they're too low they will sound a bit more dry and dull, especially on carpet or big rugs, too high and they can get too reflective and reverby/bouncy, reacting with the room and sounding less articulate/focused.
My center channel is lower than my mains to fit below my projector screen, but I designed it with an angle so that it also points right at my ears or just above. They do make specific center channel stands as they are usually much wider than your mains. Also, if you have a tv in the room, some people actually put their center channel on top of the tv cabinet, maybe with a towel or some kind of fabric/material above and below the speaker to avoid scratching the speaker cabinet, with the tv sitting directly on top of the center speaker. Ideally for movies, you want the center channel as close as possible to the screen to anchor the dialog to what you're seeing on screen. Makes it more life-like and natural.
From what I've read, for movies, it's best to have the surround speakers a little higher, maybe two to three feet above your ear height, so that they blend better and aren't too 'pointed', but with music a bit lower, like maybe a foot or so above, but you still don't want your surrounds pointing straight into your ears. I sort of split the difference between higher for movies/lower for surround music.
Anyway, blah, blah, blah, just trying to help throw out some ideas to help get yer nanners rockin'!
Congrats again buddy!