dont use mirical grow it has slow realease ferts in it.the better the soil the beeter results you will get,plagron,john innes or foxfarm are a few but dont use miricle grow its not any good unless you know how to feed using it.and yes you can just put the germinated seed straight into a 3 gallon pot but the plant grows better imo if it is in a small pot when in seedling and then a 2 gallon for veg and into a 3 gasllon for flower this prevents the roots becoming bound this may not happen when it goes straight into a 3 gallon but it has been known to happen so better stick to what you read when you start out as you will get better results and remember its fun so enjoy it .hope this helps the postman.