If you haven't already, you can buy a 50 lb bag of sand from toys r us. About 20 lbs fills one speaker. My pair didn't come with a plug either. I used several pieces of shipping tape to cover the bottom port, an actual plug would be much nicer just not sure what to use.
If you have your speakers on carpet, I think the spikes that fit need to be m1 size. Spikes would allow you to adjust the rake angle, tilting them back so the midpoint between the tweeter/woofer is aimed at the ear should add some height to the soundstage and make them sound a little more immediate by reducing the suckout from 2-4khz somewhat.
As for positioning, in my experience these speakers sound best farther away from the back wall than most others. They work well in my room about 19 inches from the back of the speaker to the wall, but every room will be different. Mainly, it's about tuning the bass output from the port to your liking, getting the bass right will help the midrange and high frequencies come through nice and clear. I have mine facing straight out with no toe in, as I like them best that way, but you can try to toe them in until you can see about 1/3 of the side of each speaker from the listening position. The best advice I can give about positioning is to simply experiment.