PVC sleeves work great over wooden poles. You can use Rustoleum for plastic to paint or colored electrical tap.
JiminPA is right - you really need to sand off the loose stuff or your new paint will just end up coming off when the old stuff does.
For white I’d use KILZ - made to resist moisture & mold. Relatively cheap & come either oil or water-based.
For striping I recommend the Dover tape - I have a set of PVC poles that are at least 15yrs old and the stripes still look darn good!
