2. Traditional and simplified characters, generalized traditional and simplified characters are a form of variant characters, in which strokes are mostly traditional characters, whereas strokes are less simplified characters. This phenomenon has existed since ancient times. Simplified characters in a narrow sense refer to simplified characters officially promulgated by 1956. Simplified Chinese characters are popularized in Chinese mainland, while traditional Chinese characters are used in Hong Kong and Taiwan.
Variant characters, variant characters are because of the confusion of ancient Chinese characters, and there are many ways to write a word.
This can explain why many words are written differently in different books. They are just variants of the traditional Chinese characters corresponding to this simplified word. General publishing institutions will regulate this, so the variant of a word is relatively fixed and countable, so don't worry too much.
3. If you want to learn traditional Chinese characters systematically, you can only accumulate a lot in peacetime. If you know a few words a day, you will get something for many years.
4. Reference books can be selected from books published by the following publishing houses:
Commercial Press, Zhonghua Book Company, Shanghai Ancient Books Publishing House.
The above is my personal opinion, hoping to help you.