1. There's no reason for Moria to be a Shichibukai. Why would the government send a Shichibukai to float around, terrorize the Florian Triangle, and make zombies? I have no doubt that Oda will explain it, but I'm also sure it would've been easier on him not to make Moria a Shichibukai.
Considering the whole Crocodile situation, it's fair to assume that the World Government tends to just let the Shichibukai do their own thing without too much supervision so long as they leave the World Government and Navy alone.
In Moria's case, that apparently means hanging around the Florian Triangle and making a crew of zombies.
2. Brooke has (maybe) joined so quickly after Franky. It seems Oda is now in a rush to fill out the rest of the crew.
Not really; as others have pointed out, most of the crew joined fairly quickly.
3. I have heard that Merman Island, which is next, is halfway along the grand line. There is also likely to be another Shichibukai there.
Fishman Island is next along the Grand Line, sure, but that requires that the Straw Hats immediately head there and aren't delayed by something else after they leave Thriller Bark. I would seriously be surprised if the Straw Hats don't visit Impel Down at some point or other seeing as how Oda introduced the concept; if they go much farther into the Grand Line, they'll bypass it.
Not only that, there's always the chance that they'll leave the Grand Line, whether by accident or intent, and take a trip into one or more of the Blues.
Beyond that, there's bound of be another short arc or two in there where we look in on the other major characters of the series like we did back in Jaya and during the Water 7 downtime.
These three things indicate to me that we might have hit a turning point. I think Oda is done wasting time and will now proceed directly to One Piece.
Well, I don't know that he's wasted that much time really, but even if he doesn't, it'll still be a very long time before they get anywhere near the One Piece.
They're still half a world away from Raftel geographically and an indeterminate amount strengthwise. Don't forget that there are plenty of obstacles in Luffy's path even now. Several Shichibukai, the Navy, the unknown Yonkou, and the New World itself. Of course, those obstacles probably aren't as daunting as they used to as I have a strong suspicion that Teach is going to help pick up the slack from here on out. If nothing else, he has dibs on Whitebeard.
Foxy is one,
Well, hold on a minute. The primary theme of the Davy Back Fight was Luffy's willingness to sacrifice himself for others, sure. But think for a second about what character interactions we saw during the various events. Who was Luffy hanging out with during that arc? Who did he entrust his hat to? What happened between those two characters almost immediately after when Water 7 started?
Little Garden another, Sky Island is arguable, too.
Little Garden is probably the closest, though I think it's the first arc where we get a real idea of what Usopp means by Brave Warrior of the Sea.
Skypiea, though, is far more important in retrospect that currently believed. If they don't visit Skypiea, then where do they get the money to buy Thousand Sunny? For that matter, is Merry even ever damaged enough to require total replacement if they don't ride the Knock-Up Stream to Skypiea?
Of course, it also prevented Ener from commiting genocide again, but that doesn't really effect the overall storyline to be honest.
I think you could have skipped from Robin joining the crew to the Puffing Tom train station and not notice a thing (a noted exception being Aokiji's appearance, which had nothing to do with Foxy).
Don't forget Jaya, which is arguably the single most important arc in the entire series in hindsight. More characters that were critically important to the storyline were introduced in that single miniarc than any other before or since.
In any case, new enemies were introduced and immediately beaten down with no change to the overall picture.
Aokiji, Doflamingo, Bear, and the Blackbeard Crew have all been introduced and have not been beaten. Sure, they only fought one of the them, but it was the single most lopsided loss in the entire series as one person steam-rolled the entire crew. Of course, if they had swarmed Crocodile, the same thing would have happened then too.
The only other person above that they could have fought would have been Luffy and Zoro versus Jesus Burgess in Mocktown or the Straw Hats versus the Blackbeard Crew south of Jaya. I tend to think that either one of those fights would have proven to be a spectacular disaster for the Straw Hats.
In fact, someone has already suggested this, but I think that the Strawhats will get a new member next arc and Luffy will declare the crew filled in time for the New World.
Even with Brook and Next Person, that'd still leave them short of Luffy's declared intent of ten people. Well, unless they count Sunny as a crewmember.
Then they'll methodically beat down the remaining Shichibukai, the Yonkou, Blackbeard, Smoker, the Admirals, maybe Buster Call, Dragon, Coby(?), and maybe a bounty hunter or two. Surely that's enough to get OP up to 1000 chapters if each gets its own arc.
Some of those may occur at the same time though; Zoro and Mihawk might well happen while Luffy fights Teach. Smoker's a given, though I don't know that all three Admirals are.