Slow lifts can make you stronger.
In martial arts, we say to train the way you fight. Lifting is the same way. Lifting slow and making gains still makes you stronger. It won't develop your fast twitch muscle though, which is the stronger fiber. Consider mixing it up.
You will definately need a squat rack.
And you are right, you do not need whey, but if you want to get to posting HUGE numbers one day, you will either eat a tonne of real food, or concentrated protein like whey. Both will work. Many power lifters go for raw milk in great volume if they can get it. So do bodybuilders.
Another aspect of squatting not often appreciated is that it is largely skill based. A lot of it is learning to deal with that heavy load. High reps at a lower but challenging weight can also help. Also variety and use of overhead squats will help your core adjust. This will be important when you hit bigger numbers.
Do not stick to "one way to squat" and "one speed to do it", the body thrives on a bit of variety.
All the best and good luck!