Apart from the I/O packages for each instantiation, what is the rate of lines of code increase when converting Ada->C? Also, are there any options in Ada-C/C++ Changer to reduce this increase?

It varies from 1.5 to 1 to 3 to 1, depending on the complexity of the Ada source code. Heavy use of string concatenation and dynamic aggregates produces more C code, since C doesn’t really have any equivalent to these.