If u use same Bnet for all accounts u benefit looms and the lvl100 boost is usuable on any of the accounts.
My doings is going with a high lvl chars and then boost the other accounts lvl to 90. if u raf smart its speedy
u might have to relog sometimes to get the 50% discount to pop on a new account.
My setup is that i bought 1 account more for granting lvls. had 2 before with high chars so lvl 3 +1 meaning for every 2 tems to 90 i get one team for free (grant 45lvls per 90 char)

And if u have the time to farm gold u only have to pay for 4 accounts. if using same bnet for all of them. and still u have some tokens left for use a bad month

Guild wise it might be possbile to make a crossrealm guild ? would be nice to try this out. easier acces to mboxing people if they atleast can have one char in the guild for online events chat etc.

Currently running on eu chamber of aspects (pve) server. so when lvl is done ill crossrealm for wpvp.