been experimenting a bit with the medium, different soils, Plagron and biobizz Etc.
but found my local plant school/nursery have a good organic seedling mix (compost/worm casting) that cost less and I can pick up right around the corner
but any good fluffy soil (I prefer organic or I might as well go for a hydro set up) will do, most important is that you get the PH of your soil right (between 6 and 7) beside that you need a light and airy medium for your MJ as it don't like a compact medium that keep moist for too long, stuff like coco fibers and Perlite will do, I even used pebbles/hydro stones/leganuts anything that keep a good airy and drainable soil (remember some good drain holes in the bottom of your pots as well)
the Lime I use to get my medium up in PH a bit as the seedling soil is a bit low at around 6,2 and I mix coco in it as well (PH6) so I use like a te spoon of Lime, well actually Mearl (oceanic lime about the same but also full of trace elements) per 5 gallon of soil along with a few spoons of dry Bat guano
tho I start em in some pure seedling soil with a pit of perlite and/or coco, the guano I use in my flowering mix, that I mix atleast a week or two before I plan to use it
I normally do two repots, after the Cup`s, I use 2 gallon as its what I have 1 or 3 can also do, and before I move em to my flowering room I repot em agin like a week before the move in to either a 4 or 7 gallon depending on how big a plant I have (how long Veg time) tho I still flower clones and Auto`s in the 2 gallon`s
Edit: and I of course also top dress with it, mostly just the Bat guano around week four but the mearl also come in handy if you experience a PH issue, but be careful with it, can easily fuck up more then you fix, so agin a ts of mearl and a few of the guano is what I normal use, less is more,
beside I just use normal tap water with a bit of epsom salt now and then and in flowering molasses