Humidity should be 95-100%. Beware, as humidity meters are notoriously innaccurate. You can calibrate them using the 'Wet salt method'. This basically involves placing them in a sealed plastic tub with a glass of almost saturated salt for a few hours. They should read 75% humidity.
The dome does help keep the humidity high. Also, spray the leaves with water with a fine spray twice daily.
If you must use soil, I would use seedling and cutting compost. However, I much prefer root-riot cubes. They aren't expensive.
Watch out for 'Damping-off'. This is a fungal disease (visually obvious) that starts right where the stem meets the soil. If you see it, get the cover off straight away.
If all goes well, when roots or new growth start showing, slowly open the vents on the dome, then entirely remove the dome over a period of time (a few days). You have to slowly acclimatise them. Same when they go in the big room. Start off away from the light and slowly move them closer.
Genearally, you would not feed until they go into the big room unless using an inert substrate, in which case you might feed at max 25% normal rate.
If it doesn't work, don't give up. Cloning takes practise.
Good luck.
... (And ill take good care of them) 
So a humidity dome isn't a good idea?... How else do I get the humidity up then? 