I can speak to the first question, but not to the second. Even then answering only the first one authoritatively is surprisingly hard. Most scholarly sources on pictograms in comics seem to be primarily interested in how they are used and less in how this usage historically developed.

The story that is mostly related in some of these sources is that the 'idea bulb' originates with the 1920s (animated) cartoon character "Felix the Cat". However, I have not yet found one of those claims that actually gives a concrete source of any specific "Felix the Cat" cartoon. I myself was rather astounded when I first read the claim that the 'idea bulb' originates with "Felix the Cat", since I am quite familiar with the source material and am unaware of any instance that would closely resemble a contemporary 'idea bulb' pictogram.

There are however some possible precursors, which might have given rise to this misunderstanding.

Firstly, Felix the Cat indeed did establish quite a few pictograms to illustrate thought processes. The most common one is probably a question mark, which pops up above his head, whenever he has to solve some kind of problem. He is also noteworthy for his frequent ability to interact with these pictograms. He frequently uses the question mark to solve problems, e.g. he uses it as a golf club or as a crank to start a motor.

Secondly, Felix does have an interesting relationship to actual light bulbs. The 1925 short animation "The Cat and the Kit" is actually an advertisement for General Electric's Mazda light bulbs for cars. It depicts Felix struggling with malfunctioning bulbs from other brands until being finally saved, when he switches to Mazda bulbs.

Thirdly, in the 1936 short "Bold King Cole" Felix is repeatedly struck by lightning. When his head is struck, it transforms into a giant glowing light bulb, which he can switch off by turning his nose. In this instance his head literally becomes a light bulb and there is no connection to him having any new idea or insight. It mainly functions as a visual gag.

As I have stated before, none of these instances actually constitute a proper depiction of an 'idea bulb', though they might suggest why the concept became associated with the character "Felix the Cat".

The first instance of something that actually resembles an 'idea bulb' is -- as far as I am aware --- in the 1935 animation "Betty Boop And Grampy" by Max Fleischer e.a. In this the character Grampy dons a thinking cap topped with a light bulb to help Betty solve problems. As soon as he comes up with a solution the light bulb illuminates. In this instance the light bulb is not actually a pictogram, but a diegetic object. However I would argue that it is functionally identical and aesthetically very similar to the contemporary 'idea bulb'.

Note: This answer largely constitutes original research, and actually contradicts published -- albeit unsourced -- opinions. I am not sure of this subreddit's stance on this, so if I am breaking any rules please let me know.