Hardware to make good sounding podcasts

I myself use a Zoom h4 as an audio interface. It's nice because it has two decent sounding microphones already, but also has Two XLR inputs for Good microphones. That's not really what you sound like you want though. What might serve you better is something like one of the Scarlot audio interfaces which have several a varying number of inputs and outputs depending on model. I've heard good things about these from professionals, and they're reasonably priced. Speaking of reasonably priced, I have me a Rode NT1 microphone, which is reasonably inexpensive but is still of quite high quality. Has a pretty low noise floor too. Also comes with a pop filter which is quite effective as well.

The FocusRight interfaces seem very nice. However, I think it's worth considering how professional one really needs to get, considering that podcasts are generally only listened to once. Behringer is sort of the value brand: same specs as FocusRight and equivalent models for various numbers of channels, but the 2-channel Behringer is $60 compared with the Scarlet 2i2 at $160. I have the Behringer mentioned, and it's an unassuming steel case with lots of buttons and dials, phantom power, etc., and combo TRS/XLR jacks. It'll work just as well as the FocusRight in terms of SQ and operation. I find the preamps possibly a little hissy, but honestly the self-noise on microphones is generally going to be greater than those on the interface anyway. Plus, Reaper is pretty good about removing hiss, without "underwater" side effects so long as it's just a foreground voice in a quiet room and not a complex layered background.
Personally, the interface approach didn't work for my use case, since I record college courses for online distribution and I have to walk in and start recording with virtually no setup time. USB mics were a far better option for me, and I grabbed a Blue Yeti for under $100, plus an Audiotechnica XLR/uSb dynamic AT2005 for doing voiceovers at home.
Off-topic, but if anyone was wondering about the newer Logitech Blue Yeti Nano, forget about it from a blindness standpoint. The software was completely inaccessible, at least when I installed it on my PC, and I get the sense that adjusting levels in Windows is not the same thing as adjusting levels through the software, judging from what I saw when using the Nano on the IPhone. The older Blue Yeti is fantastic, though. I'd say grab one before Logitech takes them off the shelves in order to push their value-priced plastic nano and their overpriced Yeti Pro.

On the no-longer-made 1820, are you needing to record an entire big band at once?
"18 Inputs / 20 Outputs"

If you're wanting to record two people, each on their own microphones, then you need two channels. If you want to use most condenser mics that require phantom power, then you need the ability for 48V phantom power on both of those channels. If you use dynamic microphones or condenser mics that have their own batteries, then you don't need phantom power. Condensers pick up everything throughout your house, essentially, so dynamic microphones, where you have to get right up on it at about 1-3 inches, don't require phantom power and, as a consequence of their lack of sensitivity, don't pick up the dog scratching itself two rooms away or traffic on the street. Mic technique with the condensers is to be about a foot away and keep the gain down to minimize ambient noise, but it's still much more than on a dynamic cardioid. So, dynamic mics might be what you're after: they're cheaper, more rugged, and can be plugged into any type of mic jack, though you may need a cheap adapter. I use my AT2005, for example, plugged directly into an Olympus pocket recorder, even though the mic has an XLR connector. The Behringer UMC-202HD I mentioned earlier has phantom power on both channels. And all these interfaces operate as USB audio output from the computer, plus have line-outs to go to powered speakers or whatever.
The only wrinkle is your stipulation to be able to also record from an IPhone. If you want to record directly from any device that has an analog output jack, then you plus the device equal two channels, so any two-channel interface can still be perfectly adequate.
But Iphones no longer have analog output jacks. That makes things very tricky. Just using a condenser microphone and letting it pick up the IPhone speaker is a perfectly adequate solution, IMO. But, ok, let's say you want high-fidelity broadcast of your IPhone on a separate track and you're recording on a computer. One option is to have an interface for the IPhone itself, and the cheapest route there is the lightning to 3.5mm cable that comes in the box, plus a patch cable. You'll hear the Iphone output while monitoring your interface on headphones. Most interfaces have 6.3mm jacks, so a little 1/8 to 1/4 inch adapter fixes that. I have a drawer full of them.
Another scenario: you have the interface plugged right into your phone or Ipad and you're wanting to demo an app on the same I-device. Now your interface has taken over VO output and, unlike on Android, there's no way to choose which device gets VO output. I think that's where the Yamaha AG03 or AG06 loop-back feature could be useful. But I'd just use a computer to record, personally, since it's got Reaper running on it. Keep in mind, too, that a lot of interfaces draw too much power for an Iphone or Ipad. Even the yamaha requires a separate USB battery, though they include a handy extra USB port for the purpose, I think.By the way, as I was idly perusing interfaces today, I saw one that has two or four channels of input plus bluetooth. So that's another option for device connection. No bluetooth output, but it does let you record a computer or Idevice directly that way. Can't remember which brand it was. Pyle, maybe--another value brand.

Let's say you want high-fidelity PC output so you can demo some software or troll a YouTube video. Same story as above, since all computers I know of still have headphone jacks and you can tell Mac or Windows to use the native device for output while recording through your interface. But if you want to not do this loop-back with the cable, there's the program HiJackThis to grab the audio directly, and probably lots of other ways to do it without any extra apps. That's a Googlable problem. Or, again, the Yamaha mixer is designed to feed the USB output right back through the USB cable along with your inputs.
Hardest thing about shopping for interfaces, aside from understanding what jacks they actually have, is the type of jack. There's 3-pin XLR, aka "balanced," TRS or tip-ring-sleeve, which is unbalanced, and mic-level, line-level, and high-Z, where "z" here is for impedance and refers mainly to electric guitars. For example, the Behringer UMC-22 has two jacks, but one is mic and the other instrument; whereas the UMC-202HD has two mic preamps.
HTH.

Hi Voracious. I use the Zoom as a field recorder, and a USB interface. I totally know what you mean about trying to figure it out. I can see the controls a little, but I need a magnifier to do so, so it's not fun. Using the Zoom as a USB interface is very easy though, even if you can't see what you're doing. The amount of times you have to turn a dial or press it are set in stone and are easy to remember. There actually is a Visually impaired guide to using the Zoom H4 on the internet though. It was rather helpful, though I don't think it covers the advance features of which sadly there are quite a few. The thing I like about the Zoom is it has 2XLR inputs with phantom power, as well as its own built-in microphones which, while not as good as a high quality XLR mic, are still pretty good, especially for stereo field recording.