Are there enough ways in which to earn skill points in Shadow of War that make it possible to obtain all of the skill points from all of the 6 main sections in the skill menu or do I need to carefully choose which skills I pick to make sure I don't miss out on some of the good ones higher up on the skill tree?
No. The level cap is 60. There are 88 skill tree upgrades. You can unlock all of the skills but not all of the upgrades for those skills. Choose wisely.