1) yes and no. Plenty of people manage to go it alone, it just takes a bit more dedication and grinding (so much more grinding). A good team of four online hunters can harvest monsters with much greater efficiency, so there is a point at which having online access becomes a real blessing.

2) Basically. You pick your quest and go on it, you just have up to three other folks running around with you. HP for online monsters is scaled based on the number of people in your party (so you can also go to the "Port" even if you're not online, and farm "Port" quests, and it won't be like you're trying to kill a monster meant for 4x as many people), but the scaling is such that 4 people are still better than one even if the monster has that much more HP.

3) Yes. The game is only 11 months old after all (feels like longer to me, but my life's changed a LOT since i started playing MH3U...)

4) More like the dragon. There are only 3 monsters really like Lagombi: Arzuros and one whose name i can't remember that acts like an armadillo. Rathian (i presume that's who you mean?) has two subspecies, and her brother Rathalos also has two. More monsters are like them in size and power and general ferocity, with a few that are even bigger, Deviljho or Alatreon, or larger still: Dire Miralis, Jhen Mohran, and Ceadeus/Goldbeard Ceadeus (and Hallowed Jhen Mohran)

i guaranty you will spent atleast 300+ hours of gameplay.It's really very enjoyable and addictive specially hunting and chating with other players online

1) Easier to get in the Port than in the village, at least initially. Eventually they let you buy them, but at first you have to mill them from herbs and Blue Mushrooms. 10 is not enough later on, but you can also make Mega Potions and so be carrying 20 healing items at a time.

2) Strict limit of 3 per quest, which is the only bad side to playing online: if there's some major attack that wipes out three of the four players at once? Game over.

3) No, no reset. It all keeps going.

4) Ludroth, Gobul, Lagiacrus, Plesioth are fought mostly underwater, with some land in the mix. Ceadeus is fought entirely underwater and is the "final" boss of the village (though not really).