The planets are only good for 1 thing in combat: the gravity wells they generate. However, there cannot be more ships than there are planets. (I don't know if asteroid belts count or not.)
Asteroid belts, they do a few things. They produce a gravity well on the hex that an asteroid belt is on, ...
and they also act as natural scrambler zones, so that if a ship is in them then no ship can see it and vice-versa.
.God here - Note this is no longer true, during play test it proved far too powerful. Is it still in the rules, I hoped I had deleted it
...(Useful because you have to see the enemy ship to fire an attack drone, which constantly homes in on it's original target.)
Combat mass(CM) is never seen, you just activate your scoops and pick some up. (You fill hold with mass scoops at a ratio of 1:1.) This cannot be done in gravity wells, so use that to your advantage and beware. (Avoid gravity wells if your running low on CM, and use gravstars to keep your foe from getting CM.)
DL is gained by sitting in a gravity well(GW), which are those colored hexes you see around planets andwhen you use gravstars.(Use the X key to see a GW's power.) If the GW power is 1, you ship will gain 1 DL per turn, if the power is 2 your ship will gain 2 DL per turn. Also, it takes a GW's power+1 to move through a GW. If an attack drone cannot move in a GW, it is destroyed. I'm not sure about other drones. But this means that if you hide behind a strong GW or create one with a gravstar, you might be able to avoid a drone.
A word of caution when firing a drone: No matter where you and your opponents are, you can all see the path a drone takes, from when it is launched to when it reaches it's target. That means fly like your trying to escape a blackhole when you launch drones! (I know it works for attack drones and beholders, not sure of the rest.)
I think that's everything I can tell you... I've got to leave the house in a few minutes anyway to go to church, ciao.
EDIT: Thanks for the correction, Jonathan. Also, I had said asteroid belts produce a gravwell with a power of 1, when actually it is not limited to only 1. (I just encountered an asteroid belt with a gravwell with a power of 2 in the demo.)