Are you looking to trade it in for a new ship then?
If you're wanting to get into combat, I'd suggest the Vulture, by whichever means you want to purchase it. It's very nimble, packs a punch and can slip out of danger pretty quickly. Not to mention it looks great.
Costs somewhere between 4.5-5mil I think
If you think a 4.5 million Vulture (and afair even the buy price is higher) is combat worthy or that anyone should wait for the Vulture before they go for combat then you have no idea what you are talking about.
An A rated Vulture costs more than TWENTY millions. Twenty. You get an A graded Imperial Courier for half as much that is almost as good if not better if competently built and piloted (besides being much, much more fun to actually fly). I was also taking down AI Clippers and Pythons in my Viper MK4 just fine with some practice. All you need for combat is a A/B grade Viper and to know what you can take on and what you can't. Sure, the Vulture is strong and can take on pretty much anything (to the point of being a crutch), through extremely one dimensional, boring and rather ugly to boot. I will gladly take on player controlled Vultures with my Courier, never gets old when they realize that I got the shield strength and power of a Python, enough Shield Cell Banks to last a long time and I am ever so slightly more manoverable and much faster so once I am on their 6 they panic pretty fast.
Now that my Cobra is nearing completion and I reached the merchant rank I really want to do more fighting. Don#t know which ship to aim for next. Would a Viper MKIV be a significant upgrade just for doing combat or should I aim for something more expensive? I mean a Python would be cool, but 56 million is still far away for me.
I went from the Viper MK3 to the Viper MK4 and then the Imperial Courier. Viper MK4 is a good upgrade over a Viper MK3 and a Cobra MK3. Sure, you'll trade in some jump range and cargo capacity, but you still got enough jump range to get around (I was crossing pretty much the entire bubble from the original starting systems right to Cubeo deep in Empire space with it) and if built right you will be a pain to take out. I recommend stacking hull reinforcement packages, Viper MKIVs are great armour tanks. The Cobra MK4 is pretty much a downgrade from the MK3 Cobra and the Vipers and pretty much doubles down on the trading/smuggling aspect of the MK3 version, being much worse in combat (mainly thanks to the pretty bad shields despite being a rather big and a much slower target).
You could also try out a Diamonback Explorer instead of a Viper MKIV, you can do pretty good combat builts with it thanks to its hardpoints and it's definitely something different from playing a heavier, uparmoured Viper (I actually regret not trying it out). Afterwards I'd consider gettng an Imperial Courier before tackling the Vulture. Sure, you need to grind some Imperial Reputation but the ship is definitely worth it and only costs half as much as a Vulture to fully upgrade (besides literally being one of the most fun ships in the game, if not the most fun one, period).
The Python is a long, LONG way off for you, remember that you have to buy it and then to outfit it before it even becomes combat effective. And as component prices increase exponentially with size... you'll be paying probably around 200 million Credits just for the upgrades. Just a A class power plant, power coupling and thrusters (the bare minimum of upgrades you need for combat) pushes that up to 138 million. That's without buying any weapons, minor upgrades or a better armour type. Heck, I've been playing the game for a good 80 hours and I only got about 25 Millions lying around if I include my ship and other physical assets as well. Sure, you can buy that Python as soon as you hit 55 millions, but you better be prepared to use it for trading for a very, VERY long time (because you'll have barely any money for essential upgrades like the FSD and no capital left for buying lucrative cargo, so you'll be pretty much shipping Biowaste).