I like the idea of using the two circles to show to two key interactions we see with "Our Jess" and "Mean Jess" (both times Our Jess points a shotgun at Mean Jess!).
However, my interpretation differs from yours. Jess 3 doesn't always go on to become Jess 2. Jess 3 goes overboard and returns on the Yacht. Half of these Jess's become Jess 1 and the other half become Jess 2.
Maybe "Yacht Jess" or "Original Jess" could just be termed "Jess 0" until she either gets a shotgun pointed at her in the ballroom (and becomes Jess 2) or doesn't (and becomes Jess 1).
That makes two Jess sequences:
"Our Jess": Jess 0 -> Jess 1 -> Jess 3 -> Jess 0
"Mean Jess": Jess 0 -> Jess 2 -> Jess 4
Mean Jess just dies as Jess 4. Our Jess goes on to either become Our Jess again or to become the Mean Jess (50/50).
Anyhow, that's my take. I've seen others think Jess 4 also awakes on the beach and returns to the ship with all her memories of previous loops in tact. I just can't buy in.

Thanks all for the answers.
Actually I figured it out and made a crude presentation of the Timeline:
http://oi65.tinypic.com/eju3on.jpg
The movie shows two loops:

1. Jess 1 kills Masked Jess > Turns into Masked Jess -> Gets killed by Jess 1
2. Jess 2 (who arrives with Group 2) Kills Unmasked Jess > Turns into Unmasked Jess -> Gets killed by Jess 2
   Both loops intersects each other. But the movie tells the story from the POV of Loop 1.
   And the final timeline is:-
   Jess 1 kills Masked Jess -> Confronts Jess 2 > Watches Jess 2 kill Unmasked Jess > Turns into Masked Jess > Gets killed by Jess 1 -> Wakes up on the shore > has an accident > turns into Jess 2 and goes to the harbour
   And like you rightly said, Jess 2 becomes Jess 4. It makes sense now.
   Retard Pussy Sinister_prig

#1 and #2a: Jess 2 becomes Jess 4 (Unmasked Jess). We don't really see much of what Jess 2 does after she's confronted by Jess 1, though she most likely mirrors Jess 1's actions. We know she also drops the car keys just like Jess 1 does, e.g. And she ends up back at the theater to shoot Greg. But Jess 1 again intervenes by grazing her head with a shot. We see Jess 4's actions diverge significantly from Jess 3's after that, though she somehow still gets in a similar scuffle with Jess 2 at the railing.
#2b: Every Jess that boards the ship is an "Original Jess". They're all Jess 3 after she's thrown overboard. (Jess 4 is killed, so does not return.)
#3. She sees the Triangle return first when Jess 4 is killed. Next, when Sally 2 dies. This is when she forms the plan to get the Triangle to return by killing Group 3. She can then warn Group 4 before they board. Unfortunately, she's tossed overboard by Jess 1 before she can carry out this plan.
#4. We know thing accumulate in the Aeolus loop because every 20 minutes or so, another Triangle shows up. Back on land, every morning another Jess and another seagull show up. Nothing also there will duplicate. The seagull gets killed (which does indeed pile up), but Jess re-enters the loop (see #2b), so she doesn't pile up. She does grab another locket and sweater to bring back into the loop.

The important bit that might help with your questions is the Event Matrix spreadsheet in the second link, but here's some quick answers. Carl answered them quite well, but here's some more thoughts:

1. We don't specifically see it, but based on the pattern that's established she gets bludgeoned with a boat hook and thrown overboard (just like she does to the other one), then cycles around just like every other iteration of Jess. There is a gap when we don't see some details during the so-called "mean" Jess pattern (which I denote in the Event Matrx as blocks of gray, but there's enough to established an overall loop cycle pattern.
   2.) Look at the matrix. It'll depict where they come from. All versions of Jess come from the same original source: her home. She just loops around again and again, interacting with herself due to the asynchronous overlapping nature of the loop she's in.
   3.) Exactly as Carl stated, she actually intended to do exactly what you suggest (she even tells Greg that's what she's going to do). Once she falls prey to the somewhat erroneous notion that killing them all makes them return (when in fact it's her cycling around through time that makes them return, although the events are intertwined in a way that they're related, meaning her killing everyone does result in her falling overboard and therefore with them all returning), she thinks that she can make it return again and then "prevent them from boarding" as she tells Greg (before she shoots him). But she tries to run down to the lower portal and doesn't make it in time. The pattern of her killing everyone repeats in that manner each loop.
   4.) About 70 or more loops, actually, based on still-shots where I've counted objects (and that I've posted in that OneDrive link). As you mention, Jess forgets each loop prior to re-entering it each time. As a result, she makes the same mistakes, producing similar results each time. Each environment "resets" when she loops to the past (technically, she's just going back to a point in time before things changed). However, objects that have looped around but then get stuck there don't reset because they're a duplicate of the "original".
   I think of it as being orphaned in time. So there aren't Tommy's and cars piled up because when she goes to the past that event hasn't happened yet, and those objects don't loop around in time. We posit that the seagull piles up because it's also looping around. It flies into the past then dies, becoming an orphaned temporal artifact, and therefore piling up. The stuff on the Aeolus piles up because a new iteration of it is taken there and left there, therefore piling up.
   Hopefully that helps.

I'm something new entirely. With my own set of rules. I'm Dexter. Boo.

None of this answers my questions. And if you think your post have answers specific to my questions, you may quote the same over here.
Retard Pussy Sinister_prig

Take a gander at this:
http://www.imdb.com/board/11187064/board/thread/223982092
http://sdrv.ms/MoXetr

I'm something new entirely. With my own set of rules. I'm Dexter. Boo.