It depends on the level of purity and number of reticulocytes that you need. Percoll gradients can be tricky to get good separation. Most reticulocytes express CD71, so you could use magnetic bead separation with anti-CD71.
Yes, removal of WBCs and platelets is best so that you have a cleaner population of RBCs to start with. Make sure that you have a good separation of the WBC and RBC fractions and do not disturb the RBC layer as most of the reticulocytes will be at the top.