Yeah, Neymar would have succeed him but he wasted way too much time under his shadow, he should never have had stepped there to begin with, Bayern was a much better choice for him.
I don't know. He probably learned a lot playing with players such as Messi, Iniesta, Xavi, etc.
Remember the year they won the treble? Right before their match against Bayern in CL, they had a league game (one of the last ones of the season) where Messi and Suarez had scored. Messi was in competition with Ronaldo for the Pichichi (most scored goals in the Spanish League). There was only a goal difference between them.
But when Barca were issued a penalty, Messi handed the ball to Neymar. So that all three of them (Messi, Suarez and Neymar) would end up on the scoreboard before the big CL game against Bayern, as a confidence/morale booster. He didn't care that it lowered his chances of winning the Pichichi.
After the game Neymar said something like "I will never forget the lesson in generosity Messi taught me today". Ronaldo ended up passing Messi in total League goals that season and won the Pichichi, but as you may recall Barca went on to cruch Bayern and took all three titles that season.
In contrast, during Real Madrid's league game that week, Ronaldo got pissed when one of his teammates scored a goal instead of him (he intercepted the ball before Ronaldo got it) and started gesticulating angrily, and was cursing. Real went on to lose their match to Juventus. Perhaps morale wasn't at 100%? Who knows.
And that season when they won the treble, MSN played increadibly well together. Even if he wasn't voted as the #1 undividually best player, the trio MSN were by many considered the strongest trio of all time, and cemented theirt place in the history books.
That's just one example, but I think Neymar learned a lot from Messi and the Barca players that will help him in the future.