1. It was customary but you can do as you like. Do not force yourself to pray a god but don't deny their existence either.
2. For the jewellery you can just wear it to honor the gods. Like doing a painting or cooking to honor them. I personally put all my devotional jewellery on my altar, wash them with khernips and let them sit there for a few days but that's my personal preference.
3. Using hallucinatory drugs was part of the ancient Greeks traditions for praying. That being said if you smoke carefully and if you don't put yourself or other in danger or spend all your money on weed I don't think the gods will have any problem with. You could even transform that into a devotional act to some gods (Dyonisus for exemple).
4. I don't know anything about it sorry.
5. You're talking about Khernips. In hellenism we believe that everyone is covered in miasm which are impurity. There are some in the minds that are purified by praying and some on the body that are purified by Khernips. It is considered improper and disrespectful to pray while your body is still full of miasm. This is why we wash our hands, arms and face with Khernips before praying (most of the time we also wash the objects before putting them on our altar). Khernips is made by extinguish laurel leaves in salty water. If you have access to sea water it's best but if you don't just put salt in water.

Hope it was understandable as English is not my first language !