I'd be very very careful about using high phosphorous fertilizers. MJ hands down needs twice the amount of potassium (K, the third number) as it does phosphorous (P, the second number).
https://www.rollitup.org/advanced-marijuana-cultivation/440586-nutrient-ratios.html#post5862534 <- Beansly posted this, I value Mel Frank's opinion over internet and nutrient company rumor. For those of you who do not know, Mel Frank has written a good deal of grow books, the Marijuana Growers Guide, which was written with Ed Rosenthal, is probably his most popular book.
The reason for using epsom salt is to increase your mg, which is necessary during flowering. If you are just using backyard dirt then you definitely want to do this.
Molasses is most effective from week 4 - 2 weeks before harvest. It is used as a carbo-load (I think that's hyphenated?) to naturally sweeten buds. You could just use products like sugar in the raw or any other form of sucanat, subcool is amongst the group of growers who use sucanat, and he breeds/grows fucking dank.
