Hey, yea I think sand helps in soil. A big bag that would last you about 4 grows doing 2 plants a time is only about £10, but you can make your own soil mixture. Search on here.
I don't know what N.P.K levels should be used, search.
I haven't been able to find molasses but didn't look very hard as we only decided to get it about a week before harvest. I know that it's used for baking/cooking, it's not specifically used for growing so finding it at a garden/grow shop is not likley at all. Should be in some food shops, have a browse.