Would it be hard to do this myself? What things would you advise if I were to go about doing this myself
If you can turn off the sub-panel this stuff it pretty easy, BUT, there are LOTS of idiots out there, so I don't want to encourage an idiot to do their own electrics.
Once the power is off you can test it's off with a
contactless power checker you can remove the breakers that are in there and see how easy (or hard) it is to move them up or down. You will need two slots free to add another 50 amp breaker, but there is space for it if you get
a dual 15 amp breaker, take the old one to the store to be sure you are getting the right unit. Take out those two 15's above the dual 30 amp breaker and replace them with the dual 15. That will leave one slot above and one below the 30, take out the 30 and move it up one slot and re-insert it. You won't need to remove the wires like you did when you replaced the 15's.
Then attach the red wire and the black wire of a length of 8ga Romex to a new dual 50 amp breaker and clip it into the empty space. Now screw down the white wire to the neutral bus where all the white wires are attached, and the green or uninsulated wire to the ground screw. If you are mounting a
NEMA 14-50 outlet run the Romex thru the unused knock-out at the bottom and protect it with a
strain-relief. Hook the neutral and ground to their respective screws in the outlet and the hot leads to the other two and mount the outlet on the stud and attach the cover plate. If you are going into a HPWC directly just run the wire out thru the sheetrock and follow the installation instructions on the Tesla Wall Connector.
If you are running the outlet or the EVSE some distance from the sub-panel I might hire someone, depending on how much grunt work you wanna do. Lots of knocking holes in sheetrock and drilling holes thru studs, or you can run shielded conduit outside the wall (indoors or outdoors) and then you don't need Romex, just regular 6ga wire. Maybe 8 or 10 gauge wire depending on how much power you plan to supply. If you have a 50 amp breaker and only going 1 foot you can use 8, longer you will wanna use 6.
If instead, you use a dual 20 amp breaker you can use 10ga... Smaller number is thicker/more expensive wire. I wouldn't do this. The car may try to draw more that 20 amps worth of power unless you specifically tell it not to.