Both the TR-09 and TR-08 are pretty much exact replicas of the TR-909 and TR-808 in terms of controls and features, both with a few voice control parameters added that you can change by diving into the menu.
This means that the TR-09 and TR-08 are just as similar and different from each other as the TR-909 and TR-808 are similar and different from each other.
No.
No.
Depends on whether you think the TR-808 is substantially better/easier/more fun to use than the TR-909!