I started with this movement, because my project is a top-down shooter, but I do plan a smooth movement for the next FPS addition...And a Z movement/jumping.

Until then, you can try to make it yourself, using simple key sending and modifying the movement function. The movement function just moves an entity. A simple idea is to add to it increase/decrease using a skill for every entity, saving current acceleration in it. It'll be the same (on theory) on client and server, so it shouldn't be a big change for the whole system...No need to send anything more than what is being send right now...

As for the delay and the bounding boxes, yes The bb are wrong, but I was focused on the MP part, I'll fix it some day. The delay/difference is caused by latency and cannot be avoided, unless you send more often. The better solution is to include prediction. Again, some day...