2D-MMORPG physics engine

Would it be more efficient to use Box2D collision detection for a 2D-MMORPG, or could it be more efficient to design my own physics engine? I’m mainly worried about calculation costs on a larger scale with hundreds of players.

What I have: So far I am working on my own physics engine that is an attempt at being as optimized as possible. I am using a tiled map environment and only check the tiles in the direction of the players movement(rather than checking against all stored collision tiles). Player movement is smooth movement(pixel-by-pixel) therefore collision detection happens for every round within the update() function. So far, my engine works great for collision against tiles.

What I ‘eventually’ want: The end goal is to be able to detect collisions with certain specified tiles, and also to have player vs player, player vs monster, player vs skill, monster vs skill collisions.

With that being said, should I just save the time I’m currently spending on making a physics engine and just use Box2D? Or should I keep going because maybe Box2D is too bulky for what I need it for? I’m essentially trying to go for the most efficient route possible, and am wondering if Box2D would be appropriate for games of very large scale and large amounts of collision?