For better or worse, I agree with Benny. I never flew spits to start, and, IMO, they won't teach you anything but to flat turn. Other planes force you to learn something in order to survive. Spits teach you how to pull the stick back.
It's up to you in this regard. None of us can pretend to know your mentality, so do what you think would be best for you.
And, after thinking about this for more than 15 seconds, I say take the K4. The 38 is big, and while it's not slow, it's definitely not the fastest. For a guy just starting, the speed of the K4 gives you a much better chance at surviving. If you find yourself surrounded by 2-3 bad guys, you can most likely just fly away.
Once you get the basics down, such as flap usage and energy management (which you'll need to learn to be successful in 109's and 38's), then you might want to try the 38. But until you get used to using flaps and energy, and unless you've flown other simulators, the 38 will just feel big, slow, and clumsy.
With all that being said, the plane is only part of the equation. If you want to learn and progress as a cartoon airplane driver, 95% of it is on you. Learn how to use your flaps ASAP!! Don't HO (you will learn absolutely nothing) and don't run from a 1 vs 1 fight (1 vs 1 is a really good oppurtunity to learn). Schedule time with a trainer.