Impact of unit renumbering in a 5500/5600 stack?

[GCM]

I have a stack of (3) 5520s (units 1-3 with 1 the BU) running 6.2.1 image.  I'm adding a 5650 and replacing one of the 5520s (unit 3) with a 5650 so I end up with a hybrid (4) switch stack (2 @ 5520 and 5650).

My plan is to add the 1st 5650 (factory defaulted and on same diag/imag as stack), which will be unit 4 (correct?), let it sync the config from the existing 5520 BU, power off and set the 5650 as the BU and then power back up and run the stack hybird command on the 5650.

I then plan to add the 2nd 5650 to the stack, which will be unit 5 (correct?) and then configure it to match 5520 Unit 3's config, move Unit 3's connections, and remove Unit 3.

Several questions -

1) Is this the best procedure or should I go ahead and add both 5650s at the same time?
2) The stack will consist of Units 1, 2, 4 and 5 after adding both 5650s and removing the 5520 (correct?).  What is the impact of renumbering the 2nd 5650 (the non-base unit) to be Unit 3?  Does it retain it's config and update it with the new unit number (e.g. MLT 1 members 4/50,5/50 become MLT 1 members 3/50,4/50).
3) In general I'm unclear on the impact of unit renumbering in a stack and the NTP/Avaya documenation is seriously lacking in this area.

Thanks

[Johan Witters]

Stack renumber is quite easy:

run the renumber command through cli or renumber through the EDM. The stack will automatically reconfigure according to your selection, you do not need to do manual changes..

For the addition/change of the 5600's, I think you will be faster if you build a new 5600 stack with the settings of the current stack, and adding 1 of the existing switches...

[GCM]

Thank you Johan.