Regarding the re-assembly once the trackpad is back in place, be careful when re-fitting the batteries; the adhesive which takes so long to separate may not hold the batteries to the chassis upon re-fitting. It may be necessary to use thin double-sided foam tape to ensure that the batteries are held firmly in place once again so that vibration does not cause the connections between the batteries to fail.
In addition to using the wheat bag/iOpener to loosen the batteries, I found it useful each time I inserted the plastic card under the batteries to give the card a 'wipe' with isopropyl alcohol to ensure that it didn't stick to the adhesive holding the batteries down. it also presumably eases the glue away from the batteries somewhat.
On each 'corner' of the frame that surrounds the two centre batteries, rather than 'plastic screws' mentioned by adriendavernas there are 'domed' rubber grommets. These presumably rest against the inside of the bottom cover when it is fitted thus supporting the batteries. As there were no screws underneath in these 4 positions, there is no need to remove these grommets. Agree with alex re: removing the extra T5 screw on the power board.