I have the EEVBlog 121GW multimeter so a decent enough multimeter. No power supply. Only a basic solder station, but I do have a PineCil TS100 clone on order with a full complement of replaceable tips.
OK, so essentially, you're just starting out.
As long as the hardware of the basic model has the "best" hardware and software options can be added on later I'm OK with that option. And I understand that with all forms of electronics, the "best" is only the best at that point in time and electronics is an ever evolving target.
You've given a general idea of what you're going to be doing but haven't given specifics. That tells me that you're basically just starting out. There are many excellent general purpose scopes on the market for far below your $30K budget, as others have mentioned.
I understand the sentiment behind your question. You want something that you'll never have to replace due to exceeding its capabilities, and thus which will meet every requirement you might ever have in the future.
There's likely no such thing.
Firstly, unlike scopes of the past that supplied schematics, and which used off-the-shelf "jellybean" parts exclusively, today's scopes throughout the range are highly proprietary things, and make use of many special-purpose parts. Oddly enough, most (the new Rigol scopes are an exception) of the Chinese scopes (and the Instek scopes, which are from Taiwan) are the ones that, from a hardware standpoint, are the most maintainable in that respect, because they use FPGAs for the heavy lifting, and those are in principle obtainable, though whether they'll be obtainable at the point you'd need to repair your scope is highly questionable.
The more expensive and more capable the scope, the more likely it is to use custom ASICs, and those
are unobtainium. Some lines are built like that all the way down to the low end, such as the Keysight line.
Secondly, modern scopes are more like computers than anything else. The real magic is in the firmware. If your flash chip goes south, you'll somehow need to be able to flash a replacement, which means you'll need the flash image from the original.
On the flip side, however, modern manufacturing techniques result in hardware that tends to be
very stable and reliable as long as you treat it properly, so it's rare that something goes wrong and when it does, it's often in the front-end or in something that by its nature has a limited life, like the flash chip. The bottom line here is that the long term viability of modern scopes has more to do with changes in the nature of what you're doing than it does with the reliability of the hardware.
Now, one of the obvious things about scopes is that their capabilities for the price have evolved massively over time, particularly for those scopes that can be "hacked". You can now lay hands on a scope that's capable of 500 MHz bandwidth and is very good for small signals, has numerous protocol decoding options, has digital and analog inputs, has a decent AWG, etc., for less than $1500 (the Siglent SDS2104X+). Similar capabilities with a higher sample rate but noisier front-end can be had in the Rigol MSO5074. Such capability for less than $10K or so was unheard of only a few years ago. Another scope to take a hard look at is the Instek MSO-2204EA (
https://www.tequipment.net/Instek/MSO-2204EA/Mixed-Signal-Oscilloscopes-(MSO)/). While its raw capabilities are less than the other two scopes mentioned above, it has a very fast user interface and very few, if any, bugs.
What this trend in capability over time means is that you're
far better off buying something inexpensive and highly capable, like the Siglent SDS2104X+, and growing your understanding of how to do things properly (such as high-frequency probing) as well as learning through experience the sorts of problems you'll find yourself troubleshooting, before going further. The longer you end up using your inexpensive but highly capable scope, the more capability for the price you'll be able to get at whatever point you end up outgrowing the capabilities of your first scope.
And an additional point: just because you've outgrown your first scope for some of the things you do doesn't mean it won't be useful for those things you had already been doing with it. It'll continue to be useful for those things.
What's beneficial about active vs passive probes? So far from the recommendations I'm reading in here, I'm leaning towards the SDS2104X Plus via Amazon.com.
That would certainly be a good choice for someone in your position. You're unlikely to exceed its capabilities for quite some time, if ever.
Note that modern high-speed digital buses for peripherals and the like are so fast that you need specialized equipment just to deal with them. The frequencies are so high that the probing techniques are very demanding, and making sense of the data would require a decoder that few scopes have. Keysight, for instance, sells such scopes but they are quite pricey. But how likely is it that you'll need to be able to see the signals over such a bus? My suspicion is that it's quite low. You'd have to be building something that needs a bus that fast, at which point you'd be designing boards with length-matched differential pair signal lines, proper ground plane layout in a multilayer board, proper signal line impedance, etc. This is all very advanced stuff, and (I expect) demands proper simulation capability just for the design phase, which is of course very expensive (see, e.g., Cadence, Altium, etc.).
You have the same problems with microwave RF, for the same reasons. Check out Shahriar's Youtube channel for some great videos on the equipment, design issues, etc., that are involved with signals at those frequencies:
https://www.youtube.com/c/Thesignalpath. He's also on Odysee:
https://odysee.com/@TheSignalPath:dMost of the digital buses you're likely to use in practice with, e.g., microcontrollers and such, are much more modest and easily handled by the scopes I mentioned above. I'm talking about buses like i2c, SPI, etc.
The point here is that once you get to the point where you'd need the kind of equipment to deal with gigahertz frequency signals in the time domain (frequency domain is a different thing, and spectrum analyzers that can handle that are less than $3k these days), it's likely that you'll no longer be talking about hobbyist level engagement, but rather
commercial level engagement, at which point you'll have a business with the necessary resources to acquire the needed equipment and software, or you'll farm out the work to a business with the right capabilities.
Honestly, there's so much to learn in the world of electronics that you can spend a lifetime without ever needing to go much above 100 MHz, much less into the gigahertz range. So I have to echo the sentiments of others here: start with something inexpensive but highly capable (like the Siglent you're leaning towards, a scope I have myself and like quite a lot), and build your knowledge with it. What you learn and experience will ultimately direct your purchases from there.