I am in my third season, also learned as an adult, so I have recently been through a very similar quest. It is always a good idea to invest in equipment for the skill level you are aiming for in short to medium term, rather than the one you are currently at. It is not at all surprising that you felt a lot more in control on shorter skis, and it doesn't necessarily mean that it would do anything bad to you in the long run, but you are probably better served skiing something closer to your ideal length - based on weight more than height, btw. I will echo what some already said - take lessons every chance you get. It's amazing how your understanding and skill level grow with any kind of instruction.
Also, I am surprised nobody mentioned getting boots first. Honestly, as your level grows, so will your ability to do well on a rather wide range of skis, both model- and length-wise. But the right boot with the right fit is the most important piece of equipment to invest in. Spend the time and the money on getting this right and everything else will follow. I'll ski a crappy pair of rental skis of the wrong length and do OK if I have my boots on - but I might break my neck in the wrong boots, no matter what skis they are on.
And the most important thing: have fun!