3DPrinting

I'm not a fan of paper levelling. It's my belief that when the printer thinks that it is at Z=0.2mm then it should be exactly 0.2mm between the nozzle and the bed. If you're levelling with a paper when the bed and nozzle are hot, then you're most likely going to end up "one paper's thickness" too far away, e.g. around 0.1mm for printer paper. If you're paper levelling cold, then it's possible that thermal expansion compensates for the paper's thickness, but IMO it's a bit of a gamble.

Personally I level by eye. If you place a lamp behind the printer and babystep the nozzle downwards you can see when it just barely touches the bed, and no light shines between the bed and nozzle. This has to be done with nozzle and bed heated to print temp (or just below filament melt point to prevent oozing) and you have to be careful to not let the nozzle press down against the bed. You can do a safety check by telling the printer to move to Z=0.1mm afterwards, and you should now be able to slide a paper under the nozzle. However, this method might be difficult with a mirror bed, which it looks like your printer has.

2. It sounds like you're building up pressure in the nozzle potentially due to over extrusion, nozzle being too close to the bed, or too low print temp. I would avoid touching the nozzle with the hands and use a pair of tweezers instead.

3. Metal sheet build plates should be placed on a magnetic layer that is glued to the printer carriage. Maybe you can place it on the glass, but I think there's a risk that it doesn't stay uniformly pressed down on the glass. Even a tiny air gap could cause inconsistencies in levelling.

4. No it's not normal. If the extruder clicks it means that it has missed step(s). You're probably either retracting too fast, e-steps is configured wrong, or I think it could be caused by print temp being too low, though if that's the problem it would probably skip during printing as well.

5. This is normal. When you press the tension button to insert the filament it changes the filament path, but it should return to normal afterwards.

6. Washing the print surface with soap and rinsing with warm water is the best way to clean it. Avoid touching it with your hands as much as you can afterwards.

7. Moisture is almost never an issue with PLA. I think it can go bad if it has been sitting in the sun for a very long time, but that's not a frequent problem. If you take a piece of filament and bend it as much as you can then it should not be brittle and snap, otherwise don't worry about this.

8. It looks like you had a partial clog, the procedure you describe is normal to do afterwards. The clog could have been caused by bowden gap, too low print temp, incorrect retraction settings, or something else.

Photo 3. It looks overextruded in some places, normal in some, and underextruded in one place. This could be a sign that the amount of extruded material depends on how fast the nozzle is moving, and the hotend can't keep up at higher speeds. This can be fixed by raising print temp, setting a lower top speed, and/or upgrading the hotend.

Photo 5. Looks like bad layer adhesion. Often caused by too low print temp or too high print speed.

It sounds like your print temp could be a bit on the low side. PLA is very forgiving with high temps, but if you have a teflon lined hotend you need to be careful with that. Maybe worth trying 210C for first layer, and 205C for the rest?

It is possible to print on plain glass, some even do it without heating, but using some kind of adhesive can definitely help if you're having trouble. Personally I use Magigoo which works great (on my textured E3v2 glass bed) but is a bit expensive. For a budget option you can try glue stick, but it should be a brand with high PVA content, e.g. Elmer's Purple. Some glue sticks have very low PVA content and won't do anything at all. Extra strong hair-spray, e.g. Aquanet, is also supposed to work, but I wouldn't use that if you can't remove the bed from the printer to apply it elsewhere..

To summarise, the things I think you should try:

• Level the bed a tiny amount closer to the bed, could be on the scale of 0.05mm
• 5C higher print temp, or do a proper temperature calibration test print.
• Bed adhesive
• Run calibrations for e-steps (printer hardware) and flow rate (the filament you're using).
• Calibrate retraction length using a test print. What's your current retraction length and speed btw?
• If you're still failing, print the first layer of a calibration cube and abort the print when it starts on the second layer. Take photos of the first layer and post here.

I made some printer vibrations dampener

How did you make these? Dampening vibrations might seem like a good idea, but the printer also needs to stand on a stable surface and not bounce around. Some DIY "vibration dampers" actually cause more problems that they solve.

And finally, since you bought a second hand printer.. You really should verify that it has thermal runaway protection enabled in firmware. Some people disable this as a bandaid for other issues, but it literally makes the printer a fire hazard. If you have the possibility, interrogate the previous owner about exactly how they have modified the printer. They've obviously glued a glass plate as print bed, but they might have done other stuff that's not as visible.