Well for starters, I do not believe cobras, or elapids for that matter, are a good "starter" venomous snakes. I think they are too quick and definately require special training. Not to say that viperids cant be very dangerous, but they are (very generally) not as in- your- face as elapids.
Being envenomated, however seriously, by one of your snakes is a risk that is impossible to ignore, so I understand that you want a snake that is less likely to kill you then say a mamba or a large bitis.
Having said that, I think it wise to chose a snake where antivenin, should you need it, is at least available. So it is my opinion that american pit vipers (rattlesnakes, copperheads, moccasins) are a wiser choice for a first hot then say a Gaboon Viper, a popular but largely inappropriate choice (why would any american hospital have antivenin for an old world species on hand?)
In reality, any of the snakes I mentioned can kill you just as dead as a king cobra or black mamba, and keeping hots is a gargantuan responsibilty, not just for you but those around you. Its great that you have some experience in keeping serpentines, but it is not that easy in my opinion. To understand the full gravity of these amazing animals, you need to find a mentor.
good luck,
Joe