Why is the verb ( vagyok) used here but the verb ( van) was not used in the previous sentence ( with a similar construction) ? When should we use it?
Only "van" and "vannak" get dropped in these types of sentences. All the other variations of lenne are included.
So, I understand pozitiv means positive, but in what sense? In this sentence, is it "optimistic/upbeat" like in English? Can we also use the word "negativ" to describe one's personality?
Yes, the same as in English.
A kedves miert nem jo? (a baratsagos helyett)
Do you drop the indefinite article only with professions or can it be omitted here?