This type of question is better suited for the general forum.
Are you able to customize the way your character looks at all?
Only your armor and the gender you pick at the start. As for armor, only your weapon, offhand (excluding quivers), helm, shoulders, gloves, chest, pants, and boots, can be customized in appearance and color. Your hair, eyes, etc., are fixed and there are no variants (this isn't like other MMORPGs).
And do the graphics and gameplay change from different acts?
Each act takes place in different environments so the scenery and monsters are different. The gameplay doesn't evolve much once you reach the maximum level as you have every skill and passive available; however, there are a number of legendary items with the power to further enhance skills in unique new ways beyond that.
Oh, and is there ay PvP or Dueling in popular spots?? Or is this more of a solo player game?
PVP does exist in the game in a very limited form. The mode is called brawling and is designed for players to face each other in an unrestricted and unbalanced manner. With the current addition of new legendaries and recent class balances (designed for PVE), the PVP scene has died out entirely; don't expect many players here. Someday there might be something more substantial for PVP but nothing yet.