Let me see here, such a long list and I had to search for your trim level (Se).
You have to get a VATS bypass for the autostart and I think there is module that will allow you to use the power locks.
For the head unit try here for some options; http://www.tune-town.com/Cars/stuff/...Bonneville.htm
TaylorD has the advise for high systems in a newer gen Bonne. Post for this in the audio forum maybe he'll drop by
I have removed both fronts seats in my car (to replace seat heaters) and can help out if you need. Removing them is straight forward once you disable the air bags. The back cushion though is tough because of the air bag and seatbelt mechanism.
Do you have side air bags?