Hello malangon,
Once the roots have started growing in rockwool, you can't take the plants out. Yes, Rockwool absorbs a lot of water and can suffocate the roots if it stays saturated all the time. If you don't want to use rockwool you need to start the
seeds in another growing media.
If you start seeds in rockwool cubes and transplant into another growing media, the trick is not to allow the rockwool cubes to get to much moisture, while allowing the rest of the roots to get enough moisture. Once the plants get bigger you can adjust the water level so the rockwool cube doesn't get any water at all, and the main root-ball underneath gets plenty of moisture. The rockwool cubes are small and the bigger the plants get the more roots that grow outside of the rockwool cube, the more roots outside of the rockwook cubes the less it maters if the roots inside the rockwook cubes are suffocated because the plant can get oxygen from the rest of the root system. However with that said you still don't want it to be water logged because the rockwook cube surrounds the stem of the plant, and if the stem is constantly wet, that can lead to stem rot.