Replacing old kitchen window with new construction window
Easer to remove the siding to get it out of the way instead of trying to work around it.
To save a step and less chance of leaks you can order a new window with built in J molding.
Yes you need to use caulking behind the nailing fin on the top, and two sides, not the bottom, then cover the fin with self sticking window tape, once again just the top bottom and two sides. the bottom left open so any water that does leak in can get out.
Then the siding goes back on.
The siding may or may not fit, reason being there's no way to set the new window in the exact same spot and may even be a little bigger or smaller then the old one.