When adjusting a coilover such as this...there are things you need to know. If there is only one adjustment knob, it's for both rebound, and compression. You need to balance this with the spring rates on the car for the bst overall ride, and performance. A 300/250 may be the most comfortable for street, or too heavy. If the ride is still too harsh after softenting up the damping, then you need to switch to a lower spring rate. But..be warned, go too soft or too hard and you can blow out the valving in the coilover.
Adjusting these is super easy as long as you have a pair of shock wrenches. https://www.pegasusautoracing.com/group.asp?GroupID=SPRINGWRENCH
Without being able to see how these are attached, I can't comment on the ride-height adjustment. Most coilovers like this do it one of two ways, either by adjusting the collar touching the spring up or down the shock body, or having a separate collar that attaches to the car itself threaded over the shock body.
As for having to lift the car back up after you pushed it down leads me to belive that you may already have a blown shock, with a dead spring. Contact Spax directly to figure that out. If you desire, you can measure the spring after you have it off the car for overall length, and I.D. and replace them with ones from Eibach, H&R, or Hypercoil. Hypercoils tend to be the least expensive, but perform just as well as the others.
Make sure you set things so the car is level with the car fully wet, and the driver, or equivalent in weight in the drivers seat, then, get it aligned properly, fully wet and with weight in the drivers seat to equal yours. Make sure that everything is as close to perfect as you can for the most neutral handling, and I like to set my toe to zero degrees if possible, makes for a balanced car. Another really nice idea is to get it corner weighted/banaced if you have a shop around you that can do it. Makes the car even that much closer to perfect.