# Plotting a Histogram3D with time (a file per frame) as parameter?

I've been working for a few days trying to make a dynamic histogram on Mathematica, but I can't seem to make it happen. You see, I'm fairly new to working with Mathematica and thus lack some knowledge on how it works.

First, I have a bunch of files listed in a directory as:

Step001.txt, Step002.txt, ... Step037.txt, Step038.txt, ...

Each file contains multiple hundred lines of data written as such:

x1, y1
x2, y2
...
x512, y512
x513, y513
...


I tried importing the files with the Import function:

file  = Import["/Users/.../Directory/", "*.txt"]


but it imports all the files at once without discerning them from one another.

I then tried importing them individually:

file  = Import["/Users/.../Directory/STEP001.txt"]
file  = Import["/Users/.../Directory/STEP002.txt"]
...


But I have so many files that it is not conceivable to list them all. Is there a more concise way (a loop, perhaps?) to import them all and store the data from each data set in different arrays or tables?

Second, I've tried using the Manipulate function with the Histogram3D, trying to use the parameter values as "time", for which parameter=1 is the data from Step001.txt file, parameter=2 is the data from Step002.txt etc.:

Manipulate[Histogram3D[file],{time,0,10}]


However, the Histogram that appears only shows the last file I imported at all values of parameters in a static way.

Can somebody help me? Thanks!

Creating five test files to play with, named "Step1.txt","Step2.txt", etc:

Do[
Export["testfiles/Step" <> ToString[n] <> ".txt",
Transpose[RandomVariate[NormalDistribution[1, .5], {2, 1000}]], "CSV"],
{n, 1, 5}]


Import them all into a list called data. I usually prefer importing as comma separated values (CSV).
files = FileNames["testfiles/Step*.txt"];

Manipulate[Histogram3D[data[[n]]], {n, 1, Length[data], 1}]