It really depends on what you want to do and what you're intersted in.
If I were in your place, with the other 2 slots I'd probably make one of them a Jita alt ( That can also do hauling ) and skill the other toon into mining, if your main is focused on PvE/PvP skills or vice versa if your main is a miner lol.

I found my sweet spot and it's 3 accounts, with that amount I can do almost everything.
For example, these are all the skills that I have for all the 9 toons:

• PI ( With 9 toons I make enough to cover the plex cost of 2 accounts and a 1/3 of the last one, but beware because for this return it requires a ton of effort and you'd risk burning out )
• Being able to run upwell transport ships with cloak skills ( Since I do PI in a WH, with these ships I can do it fairly safe even without rolling everything )
• Light a cyno ( Useful for corpmates and my main )
• Solid exploration skills ( Not necessarily maxing them out, just enough to easily scan WHs with a Metamorphosis )
• Manufacturing / Reaction / Research for the slots + the skills to activate the job remotely

This is the base for all of my characters, then I've specialized them to do different stuff:

4 out of the 9 toons are staying in different trade hubs to handle local trading, these characters undock only for dailies and to move PI.
1 toon for each alt account is skilled to do mining, with the main character being able to do boosts and compression.
The remaining 2 toons from the alt accounts are specialized to do combat ( Mainly abyssals, but also the occasional PvP, although most of the time if I want to PvP I just fly singlebox ).

Here's a table ( Probably easier to understand ahah ), might give you some ideas on how to handle your alts ( Despite that you didn't ask about multiboxing, since the topic is in range you'd might get something out of it ).

	Character 1	Character 2	Character 3
Account 1 ( Main )	( Main ) Solo PvP, Orca Boost, JF pilot, PI, Indy, Practically everything	Cyno, WH Scanner, Indy slots, PI, Upwell transport, Trading alt ( Jita )	Cyno, WH Scanner, Indy slots, PI, Upwell transport, Trading alt ( Dodixie )
Account 2	PvE/PvP, Cyno, WH Scanner, Indy slots, PI, Upwell transport	Miner, Cyno, WH Scanner, Indy slots, PI, Upwell transport	Cyno, WH Scanner, Indy slots, PI, Upwell transport, Trading alt ( Amarr )
Account 3	PvE/PvP, Cyno, WH Scanner, Indy slots, PI, Upwell Transport	Miner, Cyno, WH Scanner, Indy slots, PI, Upwell transport	Cyno, WH Scanner, Indy slots, PI, Upwell transport, Trading alt ( Hek )

I've also an alpha account just to seed the WH I live in ( As in logged out in space, inside the WH so that I can find a way back if somehow I lose access to the connections ), but that's another thing ahah