Purple can be from when overnight temperatures are low.........nothing to worry about.
It is not a deficiency symptom.
Purple stems can sometimes be a sign of a P deficiency, but not purple leaves.
Burned tips are usually associated with excessive feedind, nitrogen in particular, or a build up of salt in the substrate, but not like this for a K deficiency.
Defoliation is something that is rarely required and is not something that is of benefit to the plant in general.
Only in cases of controlling extremely high humidity levels can defoliation be of some help, otherwise it is best to keep all leaves.
Just remember.........
More leaves = more energy being made = more growth/more potential.