Hi Jörg,
1) Negatives can be represented by brackets by choosing one of the Number Formatting options, however if you want to show brackets for all numbers, then you would need to convert the number to string in a formula. You can also write the same formula in the 'Display String' property of the Number
2) You don't need separate formulas to show summaries at each Group Footer. Go to Insert Summary > Choose Amount1 field > Select Sum as the operation > There should be also an option that asks you where you wish to place this summary. Check On all footers from the drop-down. This will insert the summary for all Group Footers.
Do the same for all the other summaries.
Hope this helps.
-Abhilash