Before i answer any of the questions, i will start by saying thag unfortunately, the 2830 tank will not fit in the ATL1500.
On a better note - the 2550 tank, which will hold 1 sheet of 8X10 will fit, and many users have good results with them for 8X10 on ATL1000/1500.
1. No need to prewash C41 or E6, and you can program a wash at any stage with the ATL1500.
2-3. Here is a link the manual answering all of your other questions: