Shell Programming and Scripting

I have scnerio like this ,the below files comming from remote server 
It has to do infinete loop till all files arrives i.e.
if first file "file1.txt" arrives then copy  files1 related  to another location  
and sleep for 5 mins and then check for
if  2nd file comes "file2.txt" then then copy files2 related to another location 
and sleep for 5 mins and then check for
if 3rd file comes "file3.txt" then then copy files3 related to another location.Please any idea using while loop.


file1.txt
file2.txt
file3.txt

file1.txt
file2.xt
file3.txt

ex:If file2.ext was present in path then copy file2_* files to another location 
then check for another file if exist then copy those files.Any idea
.I have come up with this sample code ,I am not sure how to do looping till 3 files available.

count=0
while [$count -eq 3 ]
do
copy files which are realted to file1_*
count=`expr $count+1`
done

     Indicator files

     file1.txt 
     file2.txt
     file3.txt

Related files
file1_a.txt
file1_b.txt

file2_a.txt
file2_b.txt

file3_a.txt
file3_b.txt