All 3 questions are subjective, There is no one answer for any of these questions, just people's opinions.
And considering you created your account in 2007, you should already know the answers to your questions. However, you only have received 2 like in 8 years! I would say this is why you don't know the answers. I mean if you interacted more with other forum members you would have a better understanding of the domain industry.
Personally i don't fully trust members with zero or near zero likes, because it shows 1 of 2 things: They don't interact with forum members or contribute to the community, and or they only try to sell their domains here. (Selfish IMO)
I hope you take this as constructive criticism! Im being 100% honest, not trying to be rude at all. I know this advise has helped others get more involved.
That being said, i will give my opinion on your 3 questions:
1) 3 letter .com's , 4 letter .com's, Dictionary single words .coms', and domains that have high search results.
2) There is no one best place, everywhere you look, you can find a great deal if you have time.
3) It depends on the names you register, and is limited to YOUR imagination! When searching the drops and secondary marketplaces, you don't have to use your imagination... but your instincts.
Cheers!