oIso, could you help me with how much should I cut from the apex?
I don't have enough experience to pass out recipes. I approach these things by exercising principles (I think) I understand.
I would cut it back to one node on every branch in the top third, or so, of the tree. If there are specific ones that I can do without, I remove them (being careful to leave the branch collar where 'latent' buds reside). Then, next spring when the buds pop, I nip off the extending tip after the first pair of leaves.
If the lower branches that are being allowed to run aren't vigorous enough (by your Oct/Nov, say) maybe defoliate the top quarter of the tree and/or selectively lop off apical branches/shoots. Meanwhile, I wouldn't remove anything from the lower branches during the growing season. I often gently wire the soft tips of the lower branches about this time. I do it to save bench space; however, it may help to invigorate them (auxin flow and gravitropism).
Of course, if you are planning to redevelop the top part of the trunk to have more taper, this would be an opportune time to chop it and wire the new leader. Even then, you may need to keep clipping away at the foliage on the top third or forth of the tree for the low branches to rapidly thicken.