Yes, the fact that Gandalf was staying with Frodo the whole time up until then is something many people tend to forget. But if you look at it carefully, it makes his leaving suddenly even more ominous: what could be so urgent that he'd let the Ringbearer and the Ring out of his sight. Of course, we won't find out why it was so ominous for several more chapters, but still it's a bit of often missed subtle fore-shadowing.
Also, we see here that during the time Gandalf was there, the urgency was *secrecy*, not *haste*--obviously the reason Frodo was allowed to dally was in order to make his leaving seem natural, and more of a secret.
When reading it this time, I wondered what Frodo told Merry and Pippin about why he would sell Bag End and move to Crickhollow. Sam is in on the real plan, so he knows that Crickhollow is a ruse. Merry and Pippin supposedly know nothing,but they are very close friends to Frodo, so the reasons the rumor mill comes up with are to my mind not good enough.
[some spoilers below]
I agree that Frodo's reasons probably did seem bogus to Merry and Pippin and Fatty; they knew the truth. But for that very reason, they probably allowed Frodo to think he'd pulled the wool over their eyes. It's also my opinion that probably Frodo's excuses were not very much believed by the rumor mill either--we know how firmly entrenched in hobbit minds the stories of treasure in Bag End were. But of course, the local working hobbits are not going to call the Master of Bag End a liar to his face.
(At least that's the reasoning I used when I wrote my own "Conspiracy" story.)
They know Frodo too well to fall for the 'running out of money'. And why would Frodo want to settle in Crickhollow permanently when he has beautiful Bag End, just because of the SBs makes also no sense to me.
Story-externally, of course, JRRT is setting up the future with Lotho and Lobelia. He needed them in Bag End later in the story, so he brought it in early on.
Story-internally, I think there was probably both the factors of haste (how many hobbits would have the wealth and inclination to cough up the money for a luxurious hole like Bag End? I think Lobelia would have paid anything at anytime to get her hands on the hole.) and also, perhaps, there was a bit of sub-conscious "bridge-burning" going on, on Frodo's part. He knew he'd *HATE* seeing Bag End in the S-Bs hands, and so by giving up his beloved home to them, he makes sure that he doesn't back out of his self-imposed exile. It's also a clear indication to me that Frodo suspected he might never come back, even at this early stage of the game.
One of the masterful things JRRT does in this chapter is to misdirect the reader. We are never shown any private conversations between Merry and Pippin, or Pippin and Sam. We are not shown Pippin's POV at all, and Sam's only very limited. All we see is Pippin's light-hearted comments. For the first time reader, this will help to make the upcoming reveal in Chapter 5 all the more surprising.
And it gives us a lot of insight into Pippin. A person re-reading this will be struck by the fact that Pippin is keeping a really major secret--he can't *possibly* be as carefree as he appears, for we know that he knows of the danger of the Ring. So we are shown here a young person who knows how to keep a secret, who is really clever, and a good actor. I think it's very significant, for example, that it's Pippin who boldly questions the Elves, for example.
It's also clear that though he's young and cheeky, he's also helpful and responsible. He's not above teasing Frodo and Sam, but he also does what he's told, when he's told.
The encounter with the Elves is very interesting as well. It's clear that Gildor knows a lot more than he tells Frodo. Why did he not warn Frodo more? Was there more behind his reticence than mere reluctance to interfere with Gandalf's plans?