You spawn at x=-127 z=416 on a small island with dirt, sand, tall grass and sugar cane and to the north an even smaller island is visible. There is no trees BUT if you swim east about 200m (just out of view with render distance: far) there is another small island with a single tree. From the tree island you can see a larger island to the south but again with no trees.
Update: There is a 2nd tree island with a single tree if you swim south from spawn island for about 300m.
Tree island #2:
On the tiny island north of spawn island there is a 3x3 hole, if you dig in the center down to about y=22 you break through (careful 5 block fall) to a huge cave system, and there is 3 visible diamond locations within like 30m. There are also lots of visible iron, gold, redstone, lapis.
Next to the north tiny island there is an underwater entrance to a huge ravine and cave system and another small entrance to a cave system (tip: use doors/signs to make underwater air pockets).
Next to the spawn island there is visible lava down in an underwater ravine but that ravine is not very big. On the other side of the island there is an entrance on the "beach" to another large cave system.
3 more visible diamond locations (so 6 total so far!!)
Update: On the larger island south of "tree island #1" there is a cave on the island (no swimming/drowning yay!) which leads to yet another huge cave system and an enormous underground ravine. In there I found 2 more visible diamond spots and a 2nd zombie dungeon. The downside is you can see the mainland to the southeast from the larger island.
I got time to play my own seed and it is pretty great. I started by swimming to tree island #1 (see OP) and got some wood but was unlucky and didn't get a sapling. So I made a boat and went to tree island #2 where I got my sapling. I quickly sailed back to spawn island before it got dark and started building. Now I got a nice house, a (very) small forest and several farms: wheat, sugar cane, melons and pumpkins (seeds from dungeons below).
Now if you dig in the south part of the island below my house (straight down, not the tunnel in the picture going south) you get down to one of several big underground/underwater ravines in the vicinity which are connected by huge cave systems.
Running around down there I found a place of interconnecting big caves where I made my underground base (this is where the tunnel in the picture goes ), and it's an amazing place. Right around the corner in the next tunnel (like 50m away) there is a zombie dungeon. Slightly above about 40-50m away there is a skeleton dungeon with 2 chests. As you can see in the picture (below in the spoiler tags) there is a mine shaft starting in the corner of my cave and inside practically just around the corner is another zombie dungeon with 2 chests. There is of course also cave spider spawner with a chest and I found 2 chests just sitting in mine shafts with no apparant spawners near them. I got lots of resources in there from chests and from mining: melon/pumpkin seeds, cocoa beans, saddles, tons of iron/coal/lapis/red stone and many diamonds.
I made a great xp/bones/arrows farm on the skeleton dungeon. Now I'm in The Nether and I'm about to farm a fortress and then later I'm off to The End.
Here is coordinates of my "underground base"-cave, I won't give coordinates to the dungeons unless people asks: