Questions about meditation technique

1. Head dropping forwards during meditation – do I need to keep it up?
2. Is it okay to meditate lying down or adjust posture? 
3. How much movement is ok during meditation? Shifting of posture when uncomfortable? 
4. Been told have to meditate on an empty stomach and not before bed as can affect sleep – do you agree? 
5. Was told need to do 40 minutes to rewire brain, is this true? 
6. Is it okay to blend with practice already have?
7. Is it okay to say a mantra like “You are safe” or “You are loved”? 
8. Is it okay to meditate whilst running/cycling/doing other things? 
9. Is it okay to have variety in meditations used?
10. Is it okay to meditate without guided recordings?
11. Is it okay to actively visualise mentally either images or words as part of the focusing on the body or breath? For example, actively imagining the inside of my lungs?