The existing dog can't be 'free fed' so the new one will be
fed the same schedule. (roughy 12 hour feedings with a nooner noshe).

I don't think I've had any dog that could be free fed. Either they're
a vacuum, or they are a fussy eater and need to be monitored to be
sure they're eating enough to keep their weight up.

We went for feeding in dog pens.

An excellent idea.

We are actually using a baby gate to isolate our cat from the dogs.

Babygates are an excellent dog management tool. If the dogs have been
raised with them from puppyhood, they seem to respect them as a matter
of course, even if they could easily jump them as an adult. Often
they don't even need to be latched in, just set "long" and leaned
against a door opening as a reminder (though admittedly I've not been
using them to resist prey drive).

Logisticaly we look to fed the new dog in the hall or bathrom (with a baby
gate to prevent the bigger established one from eatiung her food up) for
starters. *Any problems with this?

As long as you're there to keep an eye on things until you get a feel
for how it goes, I think you'll be fine. We use two sides of a
kitchen counter much the same way, each dog is fed on their side and
we can run interference if needed if they try to come around before
the other is done.

For us, it was more of an issue with a previous dog who was a fussy
eater, the other dog would come around and hassle her until she was
done. We'd have to put the food up if she just walked away. With our
new one they finish about the same time and swap places to look for
crumbs...

--Glenn Lyford