It's not glass. But they have classes there all the time. Just classic green NE water. But the good news is, no currents, and it's spring fed with no swimming/fishing or anything that'll silt it up. I'll definitely be seeing plenty of pro training before any dives. Not worried there.
But I'm going to want some form of personal redundancy before anything deep.
What do you consider to be "deep"? And why do you think you need redundancy for depth?
The primary reason to have redundant gas is for a situation where catastrophic gear failure combines with no available buddy to share gas with. Even those of us that dive doubles and undertake decompression diving do not expect such a situation to occur very often. Your buddy should be - as you progress into deeper, more demanding diving - a key part of your "equipment". I would not dive beyond 100-120 feet with someone that I did not know and had just met on a boat and the expect that person to be a reliable backup source of gas. But in practice I would never find myself in that situation. Like a lot of experienced divers I tend towards self reliance. (There is now even a PADI course for this!)
However, at that level you should be at the very least running some sort of dive plan. That means you have a forward idea of your gas consumption and decompression requirements. Not perhaps a formal plan but at least an idea of what you want to do, what is the point at which you begin the ascent and which part of your "team" is responsible for what. Who will launch the dSMB, which person uses the most gas and therefore is the most likely to trigger the ascent. Do you both run the same computer algorithm? What personal variations, age, body mass, or other factors affect the decompression obligations. Do you plan a mandatory decompression stop (you have left PADI behind now) or just a no-deco dive with a safety stop? If the latter how much bottom time is acceptable? Do you plan (both of you) to extend the bottom time with EAN? If so what are you both planning to use and do you carry enough of it? Have you made a gas management plan and will your gas supply provide adequate back up for your buddy? What is your buddy's gas consumption rate?
Or just strap on a pony with no training and think you have got all that covered.
A redundant source of gas is important when there is no buddy. Buddy separation is most likely in conditions of very poor visibility. If you are diving in those conditions then you still need a plan. What will you do if you are separated? Do you both have redundant gas sources or is your buddy reliant on you. Could you perhaps use a buddy line?
There is a huge amount for you to learn as you move on from the basics. It's very easy to see redundant gas as a "must have" and many people do, but they haven't really thought about why. People talk about not trusting the buddy time and time again. But that cuts both ways. The idea of mutual reliance is the heart of the buddy system. If one half of that "team" doesn't trust or need the other then it is not a team, just two divers that start the dive together. As soon as you accept that you have abandoned the buddy system and are a solo diver.
Nothing wrong with solo diving if you have the right equipment and training. But the one thing I would say about solo diving is that it is not generally deep diving. So your requirement for redundant gas due to depth is not fully thought through. The deeper you dive the more important the buddy becomes.
The other reason I see often that people want a redundant gas source is the fear of free flow due to depth and cold water. Again it bears some analysis. If your primary regulator free flows due to cold and depth why will the pony regulator somehow be OK? If the pony reg is better suited to cold and depth why not use that reg as a primary? If the water conditions are likely to give this problem then two divers breathing off a single first stage is bad news. However, in nearly 30 years diving in mostly cold water I have never had a free flow.
In summary try to think through what you are trying to achieve. What is driving you to want a redundant gas source and whether you really do need it. Please by all means move to doubles if you think you will want to progress your diving later on. The sooner you start with them the sooner you will get used to them and be comfortable with them.