What rules apply for collecting toy or model cars ?

I am thinking about stating a toy or model car collection. What do I need to know eg. what brands or model are considered collectables, how much some of these toy or model cars from the past are worth today , how much willl some og model cars sold tody will be worth in the future if I don't open the box etc|||Unopened model cars are always worth more. Once you open the package there's always the chance of losing parts or inspection damage to the body. Some companies are reissuing the classics from the 60's so you really need to look at the packaging.