If the blocksize is increase to 2MB will that mean twice as many transactions? Basically how much of the space is used on the standard variables found in the block?
A block begins with a header of 80 bytes, and everything else is used for transactions. So if you increase the maximum block size from 1000000 to 2000000 bytes, the space available for transactions grows from 999920 to 1999920 bytes, which is just slightly more than double.
Basically, yes; assuming that the average size of a transaction remains the same, the 2MB block size will allow for almost exactly twice as many transactions per block as 1MB.