More Newb questions ...

Filaments and the spools they use - are they interchangeable size-wise, or are there various inner diameters or custom mounting schemes of the spools to have to deal with ?

Can you buy filaments from whoever, or is there some weird Apple-like compatibility thing that induces misery ?

Are there favorite filaments for our use ? Obviously TPU. Sainsmart ? Inland ? RDQ ? Pyro ?
There's a Microcenter store not far from here that stocks all colors of Inland - easy to get at least.

Bambu Labs only offers white and black TPU, at $42.00 per spool. Looking for alternatives, and any advice.

Thanks!

Spools are interchangable. Most of them have a similar internal and external diameter but there is no real standard. The inner hole just needs to fit on the spool holder but the diameter of the holders is usually way smaller than the inner diameter of any spool you buy.

For PLA I mostly use Sunlu PLA+ filament on mine which comes in a whole range of colours and which I've never had any problems with so I just stick with it. I also use their PETG as well which works well enough for me. For TPU I use Sainsmart. I don't print using any of the exotic filament types such as Nylon, ABS or ASA due to the toxic/carcinogenic fumes they give off and not having an enclosure or a well ventilated area for my printer.

1.75mm filament size is what you will be buying. And yes, the choice are endless. Amazon is actually a great place for filaments. For TPU, I had good luck with Priline. Overture is another company with cheap and good filament.

Unfortunately, every filament prints differently. Even from the same company, the color can print differently. And every printer might print a certain filament differently.

As for mounting, most printer have some kind of mount. Including the A1.