Definitely better than the usual full plastic spool, but IMHO a step back from "true" masterspool refills. I've already printed my MS spools, switching in a new refill is easy enough, and I never bother to store an already opened refill without a spool since I store all of my filament in a drybox anyway.

Getting most of my filament from DasFilament because they are a local (German) company and offer masterspool refills. They "only" sell PLA, PETG and TPU, but so far I haven't messed with other types yet, so that's OK.

Hm, interesting that the board has a solder point for an ethernet jack, but I see none of the usual "support" components near it that are typically also required (a PHY and/or network chip). Could be that that's supposed to be run in software on the MCU, but that would require that the firmware supports/includes it.

A pretty decent and cheap choice for containers are Ikea Samla boxes. You "just" need some weatherstrip from the hardware store to create a decent seal on the lid. Oh, and don't bother with getting Ikeas lid clips, they're crap compared to the printable "ultimate Samla clip".

I have the 45l Samla box, it has space for about 10 spools of filament. Printed some infill grid as a "spacer" and just dumped 1kg of desiccant in, constantly keeps the RH below 20% and only has to be recharged 1-2 times/year.

No neutral packaging? Almost looks like they want to get their printers snatched from porches....
Anyway, congrats on your new workhorse ^^

With your budget, the typical "entry point" into the hobby would most likely be any machine from the Chinese brands like Anycubic, Creality, Sovol etc. Those machines work OK, but it's very likely that you'll find some quirks that annoy you which leads to tinkering and printing (or buying) replacement parts and upgrades. But it also helps to further understand how the printer works, which can help down the line.

"Tinker-free" printers that just work and will do so for many 100 hours (like the printers by Prusa) are more expensive upfront but don't require constant "babysitting".

Regarding software, there's a plethora of programs that can be used. To name a few, we have the open source group (OpenSCAD, FreeCAD), the 'free' group (Fusion 360, SolidEdge), the web-based group (TinkerCAD, OnShape) and many more. Try them out and pick whichever suit you.

Saw that you're already considering the Prusa Mk4, and that was pretty much what I would have recommended for your price range. Prusa machines are not cheap, but once assembled they just work. But since Prusa has an open ecosystem and open-sourced pretty much everything, you have complete control and choice on what software you want to use to accompany it, and you also can mod the printer to your liking if needed.

The Bambulabs printers some others mentioned are different in that they are a closed ecosystem. You get the printer as-is with very little playroom for modifications and the software side (slicer) is AFAIK also pretty locked down to what they ship with the printer.

For the slicer, as mentioned it depends on the printer. If you go with Prusa, pretty much any slicer will work. To name a few, PrusaSlicer, SuperSlicer, Cura...
If you go with Bambulabs, (AFAIK) you're restricted to using their slicer.
For designing your own models, there's also a plethora of programs available you can use for free. Be it CAD programs like Fusion 360, SolidEdge, OpenSCAD, FreeCAD, modelling software like Blender, or many many more.

Anycubic i3 Mega-S, bought in 2019 as my first printer and modified quite a lot since then (replaced all fans except part cooling, stepper drivers, Z couplers, silicone bed spacers), and it works fine, but I still don't fully trust it to be left unattended for more than 2-3 hours. And since it's lacking most of the newer "convenience" features like ABL (and is rather slow) I'm really considering to replace it with a newer/better printer. Hottest contenders are currently either a Prusa XL or a Voron 2.4.

If you can already hear it during normal printing, then yes, it's most likely wet filament. The water trapped inside almost instantly turns into steam inside the nozzle and expands, causing the molten filament to bubble up as the steam escapes.

Hm, not sure if it's (just) the grainy photos, but the skirt line looks pretty uneven. Is that a fresh roll of TPU, or if not, how did you store it? TPU is hygroscopic (attracts moisture), so if you left it outside a drybox it probably got wet. A quick test to confirm that would be to just extrude some in thin air. If you see/hear any sizzling/bubbling, that's the trapped water turning into steam.

General tips for printing TPU: print it slow and with as little retractions as possible (if you're on a bowden setup). You could also try slightly increasing the extrusion multiplier.

PETG has become the second "entry level" filament besides PLA because it's almost as easy to print with (just hotter) and also doesn't require an enclosure. Not as stiff as PLA and has a little flex, so perfect for prints that don't have to be 100% rigid. For example I printed a smartphone holder for my bike out of PETG with 4 "arms" that grip the corners, and it has just enough flex so I can get the phone in and out. Temperature resistance is only a bit higher than PLA.

TPU/TPE are flexibles and available in all grades of flex, the softer ones can be tough to print on bowden machines.

The "kings" of temperature resistance and toughness are ABS, ASA, PC (blend) and PA ("nylon"), but they pretty much require an enclosure and good ventilation (fumes...) and have to be printed very hot, so an all-metal hotend is highly recommended.

If companies that still used plastic spools are starting to switch to cardboard, I think that's a good thing. Not only is it easier to recycle, but probably also lighter (your typical 1kg filament spool weighs around 200-300g), so the bulk should save some fuel for transportation.

Though I personally prefer using no spool at all (during shipping) 😉 Wherever possible I buy Masterspool refills.