First I would seek clarification on what the long term plan is. Will you keep those three files and grow them as needed or will you continue to add 500 GB files as needed? The way I usually see it done is to pick the number of files upfront and to let them grow with the data. If you do it the other way you'll end up with a new file every few months.
If you can temporarily get some space allocated to the server, I would create the files for a new database, turn on trace flag 1117 and/or 1118 if desired, install your code and move all of your data using minimally logged inserts. That'll get your data nicely distributed across the the files.
The point of the above strategy is to avoid fragmentation. It can be a lot of extra work depending on how difficult it is to install your application and how data is distributed in your tables. I've never tried
SHRINKFILE (Test1data, EMPTYFILE) so I can't comment on that.