I understand your need to stay within a budget, but I’d think twice about buying an Intel Mac today.
That having been said, I’ve written about this in the past. It’s impossible to know for sure what Apple will do, but historically, Apple has dropped macOS support for a CPU architecture about two years after the last computer with that processor was discontinued. At least that’s what happened with the 68K->PPC and PPC->Intel transitions.
The last Intel Mac made was the 2019 Mac Pro, discontinued in June 2023. Second-to-last was the 2018 Mini, discontinued in January 2023.
We know that macOS 16 (shipping soon) has Intel support. But I predict that 17 (expected in fall 2025, more than 2 years after the last Intel Mac shipped) will not be bootable on Intel Macs.
Apple usually provides support and updates (at least for security patches) for two years after release. So that Intel Mac that I predict will top-out with macOS 16, should get system updates until about fall 2026.
Third-party apps will probably begin dropping support some time in 2026, with some holding out longer than others. Open source apps, like Firefox, seem to hold out the longest. I’ll let others make guesses about TurboTax.
FWIW, I use TurboTax online, which only requires a modern web browser, which will likely be available for a lot longer than supported macOS releases. The only downside is that you are sending all your information to Intuit’s servers (I don’t know if a local installation also forces you to do that or not).
Yeah, that’s a problem. If you can’t afford more RAM, then you have to figure out how much you really need, because no Apple Silicon Macs have upgradable RAM.
Many people have reported the Apple Silicon is more efficient than Intel systems, so 8GB might be adequate for running apps that needed 16 GB on an Intel Mac, but I remain skeptical. I think some of that observation is because the SSD is much faster, so swapping doesn’t impact performance as much, but I still think swapping is a bad thing (especially for SSD longevity), even if it’s not a big performance hit.
Yes. You can plug in an SSD or hard drive via either USB or Thunderbolt. You may have to jump through some hoops if you want the external device to be bootable, but if you just need it for document/data storage, there’s no problem.
As I’m sure you’re aware, SSDs are much faster than HDDs, but cost more. And Thunderbolt is faster than USB, but usually costs more. What is best for you will depend on your budget and what you plan on using it for. But that’s best discussed in another thread.
Don’t make product recommendations based on off-the-cuff statements of executives. Not from Dell, not from Apple, nor from anyone else.
Dell makes a lot of different models, ranging from absolute trash up to top-end servers and workstations. I wouldn’t recommend the models they sell on store shelves in mass-market stores like Best Buy, but if you go to their web site and know what you need, you can get a very good system for a good price.
Ditto for HP, which is Dell’s biggest competitor.
If you want a powerful PC, consider getting a gaming system. They usually come equipped with fast processors, a powerful GPU, lots of RAM and storage. But if you’re going to use it for work, you may want to make sure you can turn off the RGB lighting effects. 
But do your homework there as well. There are companies making “gaming” PCs that are selling overpriced junk. As with all things in the PC world, you really need to know what you’re buying, because marketing literature is not going to give you the truth.
If it was just a matter of a new OS version for the same hardware architecture I’d say yes.
But no patcher is going to be able to create Intel software from an ARM-only distribution.
That works because the OS releases you’re patching are all built for Intel processors. It won’t work once Apple goes ARM-only. Which I predict will happen in macOS 17.