i've got a similar process, where i need exactly 17 files in a folder that is cleared out daily.
a simple script task to count the files what i use;
string WorkingFolder = (string)Dts.Variables["WorkingDirectory"].Value.ToString();
string[] AllFiles = Directory.GetFiles(WorkingFolder, "*.csv");
Dts.Variables["AllFilesExist"].Value = (bool) (AllFiles.Length ==17);
Lowell