Assuming the quantity is in cell C3 and the data is in cells C4, C5, ..., there are two easy ways to select the data:
1 - Use the End function to select the rows containing data.
Dim Data as Range
Set Data = Range("C4").Offset(Range("C3").value,0)
Set Data = Range(Range("C4"),Data)
Dim Data As Range
Set Data = Range("c4").End(xlDown)
Set Data = Range(Range("C4"), Data)
Data.Select
2 - Use the Offset function to select the specified number of rows.
Dim Data As Range
Set Data = Range("c4").Offset(Range("C3").Value, 0)
Set Data = Range(Range("C4"), Data)
Data.Select
Method 1 stops at the first blank row.
The easiest way to copy and paste the data with the options you want is to record a "temporary" macro while performing the task manually. Then you can copy (and tweak) the code into your "permanent" macro.