Cool thing about 3 Ultimate is that the entire Online set of quest is available in solo and Local multiplayer for both the 3DS and the Wii U. You don't have to worry about the game being locked now if Capcom decides the online server is too expensive.

The devs mentioned they adjusted the difficulty curve to make it more managable, so the monsters are easier in the low rank quests (Star 1-5) than their Tri counterparts. This is slightly balance by having specific types of armor spheres being harder to achieve, example being I always have a hard time finding Armor Sphere+. I have noticed though that the jumps in rank are more clever now. High Rank Monsters put up a better fight that doesn't feel cheap.

There are many options for online, and as a recommendation it would depend on the option you want. For just general questing, once you get past the *1 rank you could potentially start the Port Tanza quests without being a complete burden. You'll need to keep in mind though that the quests in Multiplayer will have monsters introduced in the later parts of the game in the lower ranks. If you have a group you think has good synergy with, by *2 you can be fine. Otherwise I'd wait till *3 or higher for the experience.

There are Arena battles though that I could say would be good at any time, solo or groups since it uses predetermined weapons, armor and items. YOu don't have to worry about losing valuables this way, and you get to experience some of the more exotic monsters earlier this way. That and the field has very little for farmable resources so it's straight combat.

Hope this helps a bit. The game is flexible enough were my advise is only opinion. :D