I start mine off in peat pots/module things (seed compost covered with vermiculite), then put 4 of them into a larger pot (rather than transplanting) and fill around in with compost.
i think the secret is watering. they dont like too much or too little. just a tiny drop every other day does fine for me.
also, i wouldnt try to get them too big at first before harvesting, i nip them off at a lower leaf bud (to use) as they grow and they grow more and more and more as the season goes and get bigger. if you let them just grow, they flower and go to seed.
i rotate mine from the windowsil to use, the greenhouse and some are outside. the outside ones never look as nice, but always taste better (according to my italian husband)
edited to add...i always water the compost, not from the bottom (as you mentioned) as i find they dont like wet roots. when they are just germinating, i keep them damp with a light spray bottle. also, i dont think ive ever seen a basil plant 18" high without going to seed. i think a good 8-10" with good density is the best i have achieved but they need regular nipping/harvesting to keep them looking good.