Grow kits' yields are typically lower than what you would get from using a PF Tek method and using a casing method. Grow bags do indeed lower contamination rates (as there is little transfer involved) but can still be messed up.

Shrooms are very delicate and are easily contaminated. Never ever eat a contaminated mushroom.

A shroom trip (a dose of about 2-4 grams) will last typically 4-8 hours.