PayPal没有返回我需要的所有信息？

This is a follow up to: Setting PayPal return URL and making it auto return?

I now finally get a response. This is the result of print_r($_REQUEST):

Array
(
     [q] => paypal/return
     [tx] => XXPXXX7XXXXXXXXXX
     [st] => Completed
     [amt] => 1.05
     [cc] => USD
     [cm] => 
     [item_number] => NA
     [__utma] => XXX096XXX.XXX229XXX3.13XXX76XXX.13XXX936XX.1XXX397915.6
     [__utmz] => 231096538.131XXX6095.1.1.utmcsr=(direct)|utmccn=(direct)|utmcmd=(none)
     [SESS4088bf574XXX65c931XXX51XXX9e0XXX] => f8fe6XXX18029fXXX39305cXXX4aXXXc
     [PHPSESSID] => c0XXX43a9f7XXXa5XXXb2XXXf4419XXX
     [__utmc] => 23109XXX8
     [__utmb] => 2XX0XXX38.8.10.1318XXX15
)

1. Why is the invoice value that I specified like this: <INPUT TYPE="hidden" id="invoice" NAME="invoice" value="XXXXXX"> --> not returned?
2. Why is the "Fee" value not returned? I.e. How much paypal is taking as their cut?
3. Is it at all possible to get the transaction id BEFORE I checkout? I.e. Can I request the transaction ID to be called something?

UPDATE: 1. It is now returned as 'cm' after i added <INPUT TYPE="hidden" id="invoice" NAME="custom" value="XXXXXX"> 2. ..... 3. .....