Main points:
• As you probably know, the transition away from Intel to Apple Silicon (starting with "M1" chips) is major, permanent, and forward-looking. I bet you can save a lot of money by shopping carefully for a used Intel model, but you'll be trading that for years off of the desired "forever" as future versions of macOS eventually stop supporting Intel, along with new versions of software. You can still save some money by shopping carefully for refurbished or not-so-used iMac M1 models and still get the longevity.
• Mac-related announcements are expected this month, and some Macs are being refreshed with M2; a good boost. The M1 iMacs were released 16 months ago and have seemed popular, so they might be upgraded. If so, refurbished and used prices on M1 might drop, so waiting even a month might make a difference there.
Miscellaneous points:
• 16GB memory versus 8GB? My own Mac is my livelihood and I've discovered it's using about 10 to 12 gigabytes most of the time, so I'm going with 16 for my next upgrade, given that choice. A Mac won't explode if there isn't enough memory – it just means the system will take the extra moment now and then to shift data around so that the foremost task will stay responsive, and that's something that annoys the snippy pros when they're working like hackers in the movies. It's not a huge deal, but it makes a little difference, and it's a good idea for people who want to use their systems for years to think over.
• How do people get by without Ethernet? By using Wi-Fi, naturally. Just about everything supports Wi-Fi today – certainly every Mac, as well as most routers… unless your router isn't a wireless router…?
(Good luck!)