So I tired playing through the game once already but other games came out that interested me more and so now I am back to play though this and I am curious about getting the most out of my characters.

My question is how many classes can you level up through reasonably?

I ask because for example Lissa's best class is sage but I figure that she would be best going through Cleric -> War Cleric -> Dark Flier -> Sage? I might be wrong but more just curious how many classes I should try to go through before it gets boring grinding for hours.

Things usually start to slow down to a crawl after you hit your second advanced class. So base class -> advanced class -> base class -> advance class.

Also that path you set out for Lissa is a rough one. She'll turn into a War Cleric with shit for strength and an E rank in axes, and then into a dark flier with shit for mag and E rank in spears and tomes.

I don't know how to path it was just an example of what I thought after looking through the skills that would be good.

What difficulty are you playing on? This can have a significant effect on your EXP gain and what can be considered "reasonable".

Playing on normal. The path that I wrote for lissa was just a guess I don't know what path is best for her I only went with dark flier because you get galeforce which seems to be big on everyone lists of things to get.

Pick a second base class to switch to after reaching level 20, max that one out and then go to your advanced class of choice.

So Base -> Base -> Promoted -> (if I have time) another promoted?