Am i going to have problems if i create toons on different realms?

[MiRai]

When you hover over Bleeding hollow it says I am in the Ruin Battlegroup, so I can only group with other servers in Ruin. Check each of your characters that way.

If you play on North American servers, then you can group with any other player from another server also based in North America, and not just the Ruin battlegroup. The concept of Battlegroups was dropped a long time ago, but grouping with different regions has always been restricted.

However, the Oceanic cluster isn't necessarily considered a different region entirely because you can still have BNet friends who play on Oceanic servers, and you can still group with them to do LFD/LFR/BGs, but as far as I know, players from these two different regions are not able to zone between each others' servers due to the time difference and the unfair advantage that can be gained by it when jumping between two different regions (CRZ was also annoying for those being thrown back and forth between day and night when in the same zone).