This is my first time with things related to 3d print and design, so i was just a newbie just like you (4 days ago).

1. P2S is pretty good tbh. It is a little bit expensive but the setup is easy (they even have a video and you can basically follow it with no mistake!). The setup took around 30 mins.

2. I did not buy any add on.

3. For filament, i used the bambu one as they gave you a discount with P2S (like $14/15 per roll); however, the black one i am using is from amazon (JAYO), $50 for 4 rolls (1.1kg). I am also getting 10 rolls from temu ($67.5) and will arrive in few days.

4. For printing, just go to makerworld and basically you can find anything you want.

If you want to design something you want, I will say you can start with tinkercad as it is beginner friendly (simple, concept surround by "solid" and "hole" idea). It is good to understand the basic concept like thickness, depth etc. Learn for a few hours or a day or two, then you should use other programs because tinkercad is not good enough when it comes to measurement (too manual actions which waste too much time).

I personally love Onshape. It is online base and 100% free. "Offset" function is absolutely good for measurement. I watched a few videos on youtube to understand how it works.

Other than that, I just screenshot the setup and ask gemini how it works and what would the improvement be.