Agate

[Lawless 0]

so I'm moving to agate now and from what I heard you cant go back to reborn after awhile but I don't know whats coming up and and I don't know what pokemon to bring with me.  

[Edo 153]

Whatever you need, at any point in the game, there is always something helpful available. You probably don't need to get anything in advance.

 

Edit: TM for Rain Dance might actually be something that's good to have in case you can't beat Charlotte.

[Starry Knight 753]

Oricorio is rediculously good on Samson/ciels field from what I hear

But yeah try to of you want it do the stolen Pokemon quest and grab all the department store stickers you can

Do any breeding and stuff you want to do now

[Seel The Deal 44]

I'd just explore, make sure you didn't miss any major quests or event 'mons (clear out Aventurine Woods, finish the frankenstein quest down on 7th street, etc). If you do that, you shouldn't even really have much reason to go back until you're given the chance anyway.

 

Some notable things you might have missed (spoilered just in case):

 

Spoiler

Type: Null from the frankenstein quest

Litwick from the Subseven Sanctum (requires 1 Soul Candle)

Sunny Day / Rain Dance

Murkrow from the Lapis alleyway on a windy night

Meditite from Apophyll Academy, by studying with all the students

Pumpkaboo from the Beryl Graveyard (requires 1 Soul Candle)

Misdreavus from Bysbyxion Wasteland

Solosis from Bysbyxion Wasteland (enter from the cave leading to Aventurine Woods)

Department store stickers (Aventurine Woods & Lapis Ward stickers can be easily missed)

Darumaka from Apophyll Academy, traded for a Luvdisc

Tepig from Pyrous Mountain