MESA boards and firmware for mix of stepper and analogue servos

Hello,
I have a 3 axis machine with +-10v analogue servos on the x and y axis, and a stepper on the z axis.
Currently I'm controlling it with an old PCI Galil board, but would like to move to LinuxCNC with ethernet based MESA.

I think a combination of 7i96 plus 7i77d daughtercard would run the motors and provide sufficient IO. I contacted EUSurplus and the gentleman there thinks (but isn't sure) they will work, but I would probably need custom firmware.
(They also suggested 7i97 plus 7i78 as a slightly cheaper alternative, but I don't think that would have enough IO for my planned use.)

I'm  a reasonably capable programmer in languages such as c#/python with some experience in games and application coding.
I have about a year and a half programming and operating CNCs - both cobbled together DIY stuff as well as old industrial FANUC machines.
If I needed to customize firmware, how difficult a task is it likely to be?
Looking through other threads here, I get the impression that most firmware customization is a matter of including/excluding modules and changing pin assignments. Is that likely the case here, or will the mix of analogue servos and digital stepper complicate matters?

Anyone have any experience setting up a similar system? 
Any pointers or advice appreciated.

There is already firmware for a 7I96+7I77 but there is no GUI configuration support
for that combination so you would need to hand edit the hal/ini files to get a working
configuration file set.

Probably the best way would be to start with a plain 7I96 step/dir configuration
configuration generated with one of the GUI configuration tools and then
copy paste bits from a say 5I25+7I77 hal/ini file set to support the 7I77 I/O