You could copy the Customer (Company Name) lists to a single sheet and then perform a Remove Duplicates and use that for the 'Master' sheet column B.
The Customer ID would be a simply fill down, type 1 in cell A2 and then 2 in cell A3 and then select cells A2 and A3 and then double-click the lower-right corner of the selection to have it autofill down to the last company name in column B.
Then, rest would be appropriate VLOOKUP formulas. For example, in cell sheet 'Master' C2 (Sales Representative), the formula would be:
=IFERROR(VLOOKUP($B2,'Sheet3'!$A:$B,2,FALSE),"")
And in sheet 'Master' cell D2 (Contact), the formula would be:
=IFERROR(VLOOKUP($B2,'Sheet1'!$A:$H,5,FALSE),"")