i think you should do something similar to what i did:
you should take lessons at first, as people have already said, then once you learn to plane the best choice would be a 135-145 litre board. let me expand on this last one: i did the mistake of buying a very thin 130 lt board which, although in the near future will certainly pay me back, it is hard at first to get going properly, so i would advise you to buy a 135 litre board with a width not below 70cm. this will make everything so much easier and fun.
what i rented that was very similar to this was a RRD fireride 135, 248cm x 72cm, and it was perfect. i have never tried the equivalent of this for starboard which is the Atom, but i am assuming that it is also fantastic.
what i advise you to do then is to rent and take lessons, then when you start beachstarting and becoming good you buy a nice comfy freeride.
when you decide to buy your board, do not be stupid like some people i know: do NOT try to look cool by purchasing a thin board, it will only annoy you and decrease your enjoyment
72 kg, 190 cm (6 ft 3)