To those who are new to One Piece and wanted to start watching, I suggest that the best place to start is at Water 7 - around episode 230++. This is definitely a major check point for everyone's intergrity both literally and figuratively.
A lot of things has been settled on this stop, particularly, these 5 things:
1. Trust issues with Robin
Everyone in Luffy's crew was chosen by him - except Nico Robin. She's the one who presented herself, telling Luffy that she becomes his responsibility by saving her. She really is the least trust worthy in the crew since we don't much is known about her. Zoro is also right to note that she is an enemy to begin with.And with her mysterious and quiet personality, you can't help but to find her as someone suspicious.
2. Usopp's insecurities
Probably the weakest in the team in terms of physical strength and bravery, Usopp will always feel insecure - that anytime, Luffy would just leave him behind. Unless these things that destroy him from the inside, Usopp will be difficult to trust as well.
3. Finding a Shipwright
The crew is made of brave and strong people. They can face almost any enemy there is. The problem is, there's no one who knows how to take care of the ship. Usopp can fix the damages to Merry, but knowing how to avoid those damages and how to properly fix them is not his expertise. If only they had the right shipwright, Merry could have gone father. Good thing Water 7 is the land of Shipwrights and they were able to convince one to join them. I think, even if they have bought a new ship but without a professional shipwright to take care of it, they would not go very far in their journey. The ship is important in their journey - equally important is someone who knows how to take care of it.
4. Ship Transition
Theoretically, if we measure the distance their ship Merry has travelled, I would say that she already encircled the world. Measure the distance from where they got Merry to the entrance of the Grand Line and then add up the distance they travelled from the entrance of the Grand Line to Water 7 and that would be probably enough to encircle the world. One way or another, they have to let go of Merry - and this is probably the best place for that - in the land of shipbuilders.
5. Luffy's Solid Leadership
Luffy's conviction to his decisions as the captain is probably manifested best in this Arc. Whether to trust and save his comrades, or find an additional one, or let go of the ship they had for so long and buy a new one, these are tough decisions to make. Never the less, they've been made no matter how absurd they are. Like Zoro said "We are not playing pirates here." True enough.
The journey is still quite far, but this stop defined what this crew is made of.