Please, is there a web page or PDF, where I can identify basic parts esp. brackets, nuts, screws, etc. easily?
Maybe with links to products, containing them and product-Ids for reordering?
We do not have publicly available PDF with parts list, as it changes from time to time.
Everything can be found in our shop under “Totem Mechanics” category: https://totemmaker.net/product-category/totem-mechanics/bolts-and-nuts/
Each part contains unique “SKU” code if you need to reference something specific.
I tried to figure out whether I got together examples of “all possible connectors” (and I think so).
totem-mechanics/brackets
For me, as a “once-in-a-while” builder, the different brackets and their (best) usage are really hard to figure out.
I like the way of a rectangle frame with all holes up (for connecting components, modules and PCBs) - which I now found used at the side panel stand and esp. with the grove modules rack
but I do not like the idea of self threading screws for plastic, which seem to be needed with the new blue/green(?) special brackets #1…4
- I think the side stands have metal only connections, and that seems to work, too - and it also gives an option for some “lock-tight”?
- Beams are still only 400 mm wide/long? I had been aiming towards 19-inch rack-something, so 500 or better 600 mm (for a 45° diag of 400) would help (and give less residue for me - but that may be too conditional on everyone) - but maybe you have already thought of something like that?
Thanks a lot for your friendly help 
If you are referring to 3D printed plastic brackets (Brackets for Building Totem Racks for Grove, Arduino/Raspberry | Totemmaker.net), they were developed as faster alternative to metal ones.
Building simple structure like Mini Lab frame takes too much time. Using plastic ones keeps similar rigidity and decreases overall building time as you don’t need to insert a nut in each hole.
As for beams - 400mm are the longest ones we currently make. Can’t tell for sure if other sizes will be available.