>I hope you make it so that only the surface blocks are sent to the client. The time it takes to "mine" a block is enough for the latency to send the block behind it.
Orebfuscator or Spigot.
>Also, send the input to the server, and not the position/speed vectors. That way you will also get rid of the speed hacks.
What? No. You can't make sure everyone moves the same way, and this would undoubtedly lead to desyncs. If you want to make sure players don't move too fast, use NoCheatPlus or what it was called.
A far bigger issue for servers is mods like Gammabright which make all blocks have a brightness of 15, thus not requiring you to use torches or light sources, as that's very hard to work around.