No, there's no upgrades you really need at all. Stock Krakens will run for a long time with absolutely nothing done to them. There's alots of things that can be done to them, not only cosmetically but also inside the mechbox but none of them are necessary.
But I agree with Tex, I hadn't noticed that you were located in the States before. You should be able to get one of the top end manufacturer's guns for not much more then you'd pay for a Kraken. If I were you, that's the way I'd go.