I'd say soil
Water daily to every second day in the first few weeks until the old leaf dried out, then as usual every 3-4 days (depending on soil, placement and climate)
If they are important, I place them in a small pot (2", 5cm) with a mixture of 3 parts grit (2-5mm grain), 1 part sand (0-3mm grain), 2 parts peat compost (selfmade and sterilized by letting it sit at 150°C for 10 mins in the oven, to get nasty rot-inducing critters out), 3 parts akadama (red clay, used for bonsai as main soil ingredient), 1 part kanuma. Then in the middle of that pot I have a little tiny bit of humus, like a centimeter wide, just a sprinkler. In that bit of humus I place the roots. This is to hold them moist and get a first, vigorous shoot going, after that the poor water retention capabilities of grit and sand together with the kanuma will make root spread easy, rot hard and maintenance quite low.
If you don't have kanuma or akadama, substitute them with crushed up fired clay (crushed bricks or so) for akadama and pumice for kanuma. Alternatively leave them out, they should also do just fine without that, seen them grow in pure 3-8mm grain size grit but wouldn't do that if the plant was pricey or otherwise hard to get by again.
If they are easy to get more of, just take whatever well-draining soil mixture you prefer and stick as many in one pot as you want, repot one by one the ones that got big enough and didn't go down along the way.
Oh and, give them a sunny spot, best outside in summer and south-facing window in winter (If you live in the northern hemisphere), don't take the odds of leaving them outside at under 10°C.
Hope that helped a bit, maybe others can correct me at the points where my smol experience from other echeveria wasn't enough
