بسم الله الرحمن الرحيم
(1) Yes, you are owner of nisab. The price of 57 gram gold and 30000 cash is equal to 612 gram silver nisab when combined; hence zakah is fardh on you.
(2) You should know the price of 57 gram gold from the market and add 30000 cash and then pay 2.5% zakah of total amount.
(3) Zakah shall be liable on both.
(4) It is not necessary passing one year on each wealth separately rather when you turned owner of nisab it is enough that one year has passed. If during the year you owned other money or silver or gold then its zakah shall be paid at the time of paying zakah of first wealth.
(5) Yes, it is right that if you owned any amount days before the completion of one year, then you will have to pay its zakah on the same date. Hence in the question mentioned above you will have to pay the zakah of the amount on 10th Ramadan which you received on 9th Ramadan.
Allah knows Best!
Darul Uloom Deoband