First the caveat; I'm no expert. I've only cut a few gears, both with "traditional" multi-tooth cutters and "rack form" hobs. In the end, the gears worked so I called that a success.
The usual approach seems to be cut full depth at one pass. To do that requires a sturdy setup. What looks like an acceptable amount of overhang from the dividing head or rotary table will lead to flex without a tailstock or other support. It's probably going to cause a revolt but I've found a "roughing" pass followed by a finishing pass gives me more predictable results.
Using the horizontal spindle will work fine, just be aware of the amount of space you've got for support at each end of the gear arbor.
You will be well served by a power feed. Three teeth into the routine you'll be grateful! I think you'll get a better cut as well.
Good luck with whatever approach you use. Remember - you can always start over and try another way if things go sideways on you.
