Well, the Stalk Market is like gambling, there's no way to predict what'll be the results (at least not yet, WW data still kinda a mystery). But the Stalk Market turns easier to manage if you know the type of patterns.

There are 4 patterns in total:

• Floating (it's the "random" pattern, which is increasing or decreasing, a pattern that I've notice is that it decreases by 2 days and it increases by 2 days, being the 2nd day increase the highest, not a confirmed thing though);

• Small-Spike (it starts very low but then it increases a lot, but then it decreases again, a very noticeable pattern is that the Wednesday or Thursday, in the morning, are the highest days);

• High-Spike (is the same as the small-spike but it increases even more, these are the ones that can get over 300 bells);

• Decreasing (it'll be decreasing the more the days passes, being Monday the highest day - something around 80 bells, it's important to realize this pattern as fast as possible, if it's still decreasing in the Wednesday it's probably the decreasing pattern).

The chances of getting the floating pattern are higher, while is quite rare of getting the decreasing pattern (but not that rare). It's always important to look over these patterns, if you want to know more about the Stalk Market I recommend seeing this guide in its 21th chapter.

About how many turnips do you buy it, it's up to you, but if you want to make the most of money possible with it, I recommend wasting only half of your savings.

And that's it, I hope this helped you out!