How much item level we need for the new content?

[tdb]

If you have good enough gear to even enter Orbonne Monastery (i365 required) then you already have good enough gear to finish the MSQ, as well as good enough gear to enter all other non-Extreme/non-Savage content in the game.
In other words, if you can run Orbonne Monastery then you no longer need to grind for gear unless you really want to do the hardcore content.

Sure, but improving your gear now will smooth out the transition to ShB content. It hardly makes sense to stop improving your gear just because it's not necessary - unless maybe you're going to take a hiatus until ShB release. Just doing expert roulette a few times per week will earn you enough genesis to buy several pieces of i390 gear. I'd hardly call that grinding.