@sonofzell Welcome local friend!
I dive Dutch pretty regularly (mostly, actually). Given my experiences there (Dutch) with buddies (ranging from insta-, to regular, to instructor) and with insta-buddies in the Caribbean, I have come to the conclusion that
I am almost always diving (effectively) solo and, therefore, I am now
always diving with gas-redundancy - either a pony or twins.
I'm of the "sling" camp with the pony and I dive it "hot". I turn it on and test-breathe it at the start of the dive day. Before each dive, pressure is checked with the button gauge and "on" state is confirmed with a twist - I also use "Vindicator" knobs on my ponys for easy visual confirmation.
I dive with a "standard" regulator configuration for my back gas ("primary and secondary/octo") and because the pony regulator is tucked on the pony bottle, there is no confusion about which is which.
Immediate donate to an out of gas (OOG) diver is from my back-gas because
that always works - pony or no pony, single or twins. The pony is primarily for me, but would give me the option to unclip it, transition the other diver to it and then separate myself from the OOG diver if circumstances should warrant.
Roll with a slung 19cuft pony is negligible, but when diving singles, I do use 5 pounds of high-mounted (upper camband area) trim weight and I use a 2 on the left (pony) side and a 3 on the right which gives me a little counter balance).
A transfill whip is not an absolute requirement, but it is nice to be able to just top off the pony after a few rounds of test breaths. Since I'm usually diving HP100s or 120s, a quick top-off is no issue.
I'm near Norristown. If you are reasonably close and want to check out my pony setups (I have a 19 and a 40) in person and see if it will work for you, feel free to reach out. We could also probably pick up a stage kit (or the parts) up at Northeast Scuba Supply and get your bottle set up for you. I believe John (at NESS) also may have some used tank brackets if you decide to go that route.