Whoa there. This is the first car you've worked on?
Do you *know* you need to replace the flexplate, or do you have a knocking noise that you *suspect* is the flexplate? Big difference. If the torque converter bolts are loose (common, there's 4 of them in there), you only need to remove the converter inspection cover to get to those. That's a whole lot less work, and easy to do.
If you know for a fact that the flexplate is cracked, that's a different story. Either the motor or the trans will have to move, trans will be less work, but it's certainly not insignificant.
Just thought I'd offer that up before you get too far...