To be clear, you want to enter in A2 a customer number, say 3004, and then have the spreadsheet return the customer name, each product on order and quantity for each?
If so this can be done by entering just the customer number in cell A2 and the filter function combined with CHOOSECOLS will return the customer name, product and quantity columns, however I need to know which column the in MasterSheet the customer number resides.
My answer below is wrong because you have not shared the customer number column yet, but I suspect the answer will be similar and is what would be placed in cell B2. This will spill into columns C and D so ensure those entire columns, and column B, too, are cleared of any formulas.
=IF(A2="","",
(FILTER(CHOOSECOLS(MasterSheet!$A$1:$D$10000,1,2,4),
MasterSheet!$C$1:$C$10000=A2,"")))
The CHOOSECOLS returns the first, second and fourth columns of MasterSheet. Note the bolded D column is changed from the C you had originally.
The bolded column reference in the final statement, MasterSheet!$C$1:$C$10000=A2,""))), need to be changed to whatever the column is that the Customer number is stored in.
Let us know how it works.
Mike