Multiple characters have Buffs that increase the same type of stat, but sometimes they seem to stack and other times it looks like they get replaced by the other; The same goes for Debuffs, so how does that work? Is there a way to know which ones work together or not?

 Also, is there a limit to how many buffs you can have on a character? I've notice you can only see 4 active buffs on the HUD, so I don't know if the other ones are just not showing up for lack of space or if they're getting removed when a 5th is used.

 I tried to check the wiki but I couldn't find the information anywhere.

If the status caused by the skill is exactly the same, it replaces the old effect if it has a lower turn counter. When the effect is similar, like +ATK, but it's two different status effects, they're separated and don't replace each other.
Usually when the text just says something like "increases ATK for X-turns" without a value, it's the default buff, while effects with numbers are unique status effects. Most of the time they also have different icons, but not always, so I understand the confusion.

There is no limit to the buffs/debuffs. They're in effect, even if you can't see them due to the hud being "full". Which effect is being shown is decided by a "priority" value that is set for each status effect, not by turns lefts or when it was applied.

The system for the status effects is default for the RPG Maker, and nothing special for the game.

Ah I see, I'll try to find combinations that work via trial and error, I'm trying to put a team with good synergy  together and want to avoid having characters with overlapping abilities.

 Thank you for the clarifications.