have you or are you doing all quests?

anything to expect when i do them all or close to doing them all?

achievements? titles? something?

Many quests unlock important features such as the challenge log and materia melding so it's recommended to do all the sidequests you see. Other than that it's just EXP, bits of story and gil rewards, but no achievement for doing them all.

I dont remember any overall broad rewards for clearing most/all of the quest log. However, many individual quests are tied to achievements, titles, unlocks, and other rewards. So you should get a lot of things along the way, i just dont remember anything at the end.

Some quests give you minions as a reward too.
I personnaly did all of them, except the Relic and Anima weapons quests, and a few job/class quests, as some of my classes didn't reach 60 yet.

Be the very best fisherman like no one ever was. Otherwise it's a fools errand.

I'm very close to having completed all quests I think (aside from Relic/Anima weapons and a few class/job quests because some are not at 60 yet and I'm not all that into healers/tanks so they may never get done), and have greatly enjoyed most of the lore details contained therein. I'm not really into the Hildebrand storyline, so I haven't finished that bit either, but perhaps someday.

That being said... when you find a quest at level 50 called "The Greatest Story Never Told"... well, if you're not all that into the lore of the game and/or brain-teaser puzzle-type quests, skip it. IMO, the reward was NOT worth the bother. :)

Doing an entire questline in one area will change the dialogue you receive when visiting that area later.

Without giving any spoilers, I did all of the optional sidequests in a small town simply because I wanted EXP. You help everyone and save the town.

Later in the game, there was a time when I had to return to that town as part of the main scenario quests. When I returned, the people in the town greeted me by name and thanked me once again for saving the town!

If I recall correctly, the main scenario quest character I was with asked the townspeople "Oh, have you met before" and one of the townspeople said "yes, she helped us so much! We'll do whatever we can to help you."

I thought that was really cool.

I did almost every sidequest in ARR...think I was only missing the Fishing and Beast Tribe ones.
I'm slowly making my way towards the HW quests.

I like a clear map.

It drove me nearly insane, but I almost complete all quests.
I like my map clear ; )