imo, in which others which other players will disagree since everyone has there own opinion,
2 types of pve, Dungeons and mission maps.
Dungeons are usually to farm specific items and sell them, mission maps are to get normal gear and just sell those.
Here are classes that excel at dungeons significantly better than the other classes
Summoners, Invoker, Sorcerers, Destroyers. (Ninjas if they have a dragoon giving them time aura)
Here are classes that excel at mission maps
Sorcerers, Destroyers, dragoon, overlord, savages, ninjas, Destroyers, sentinels, twins.
I literally have every class at level 81+ and the only thing I can say about which class is fun is that it depends on the player. I have every class at 81+ for a reason, because I got bored of a class then played another. Until everything got to endgame so I just play whatever I feel like.
Also savages got nerfed a while back, but reverted the changes so savages are practically untouched and haven't been nerfed or buffed basically. If you find that class fun, play it.
If I were to pick the best pve class it would be summoner. Then invoker/destroyer/sorcerer then every class later.
For tips not sure what to say besides try not to spend money on the game and stay away from pvp cause it will give you unnecessary headaches. Make friends and more friends. Find a good guild and try not to be deterred if your friends eventually stop playing. Once you make many friends and in a good guild you can ask them for specific tips and so on. You can ask me, but making friends and having conversations,getting/giving help is part of the gaming experience I'm not here to take away stuff you can talk with your friends or future friends. If you have any specific questions feel free to pm me or here.