Answering all of your questions below:
For the health thing, do not create a datablock with a huge amount of health, sure it works, but it's very sloppy and the player will get a red vignette and the damage sound every time they spawn.
Instead scale damage inside the damage function, it works great.
For relative velocity, I have little knowledge of the methods used in TS, but you'd find the player objects rotation, and use that to get the correct x,y,z to use inside of either applyImpulse or setVelocity.
For the database thing, you'll want to just save every variable to a global array then export it to a file, and reexecute it when the server starts up.
Players won't need to /saveme or /loadme, it will be done automatically when they join the server