Phantasy Star Portable 2 Best way to Experience Co-op

[MNOPYZ]

Hey there ^^

Me and my brother wanna start playing Phantasy Star Portable 2 together, but before we do, I wanna know a few details about its Co-op.

Does playing through Story mode unlock more missions for Multiplayer Mode?
If it did, and I were to play Story mode on my own and be the host for Multiplayer, the unlocked missions would be available to both of us... but our levels would be wayy off sync. So that would take all the fun out of Co-op :/

Both of us playing through the story and then Co-oping using those characters isn't an option; PSP2 is on a single PC and we don't have much time together; I'd rather not waste that time on playing Story mode at the same time.

TL;DR, is PSP2 playable/fully enjoyable in Co-op without playing Story mode?

I didn't know where else to ask this; this is the best community I know that would know about this

Thanks!