The long internodes are probably going to cause some regrets in future if you leave them now. Long, bare sections on primary branches forever.
Removing the thick upper branch is a great plan but that will leave the apex running to the rear of the tree which rarely looks good. There's every chance you'll get plenty of new buds all round the cut so should be able to chop again next year to a better prospect.
The section below that top fork is also quite thick, straight and maybe even a bit long for the upper part of the tree. Depends how much more height you anticipate. I'd probably be looking to reduce back to the older, thicker trunk section at some stage.
Many of the replacement shoots you'll get after chopping such a strong leader will be fast growing with long internodes and therefore useless as replacements, especially if you chop in winter or spring. Often I have to chop all those again to get better shoots. Chopping later in spring or summer can give less enthusiastic shoots that are better to work with.
You can wire out branches horizontal if you wish. It is your tree but consider that's not how JM actually grow naturally. I have a couple that were trained lie this in my early days where trees had to look like 'bonsai' but now I prefer to grow bonsai that look more like the full sized versions so my JMs are trained with large ascending branches or trunks that then turn outward as branch pads.
Might be a little late to change this one over as the previous grower has already selected branches that grow horizontally.