Some good points there. I prefer to Bounty Hunt, but I am not opposed to Trading.
The Cobra isn't really an uprade then. It definitely won't feel like one if you've been flying a Viper. It may be a good way to get either a Vulture and/or Asp though, as the Cobra is a good little trading ship.
The next combat upgrade would be a Vulture, which flies like a dream with great fire power. Flying a Vulture alone will keep you occupied for a long time because it's so
fun (if you like bounty hunting). Getting a Vulture and kitting it out reasonably well will cost about
12.5 mil with insurance. It won't really be at it's full potential though.
If you're not adverse to trading then a good way to get credits is in an Asp. When you buy one don't trade-in your Viper, but do sell and downgrade the Viper parts (why will be explained below). To equip an Asp with D-grade modules, taking out the shield and throwing in cargo racks, will cost around
7.7 mil with insurance. D-grade modules with an A-grade FSD for maximum jump distance will cost around
13 mil with insurance.
As you can see, a reasonable Vulture and a full trading Asp cost about the same. A reasonable trading Asp is around 5 mil cheaper than a reasonable combat Vulture.
If you do go the Asp route you can make credits pretty quickly with rare and/or commodity trading. If your Viper is parked in a good outfitting station near plenty of RESs (like Gende) you should be able to get back to it pretty quickly in an Asp, then use your profits to outfit your Viper again for bounty hunting if you feel like a change. You could even use your Asp, which is pretty decent for PvE combat (depending who you talk to).
Bounty hunting in a toned down Vulture will be slower in amassing credits, but possibly more fun. It could arguably be quicker getting to a full combat Vulture via buying and then trading in an Asp, rather than bounty hunting in a Viper and then a toned down Vulture. Getting an Asp will offer more play-styles. Choice is yours though.
If you're aiming for a Python, I'd definitely recommend at some point straight out owning both an Asp and Vulture, as then you'll have all your bases covered - trade, exploration and combat - and can dip into any part of the game you feel like, when you feel like.