Found The Deal But Not Sure If It's Gold Or Dynamite

hi experts,

how it's going ? i m new to this so please help me

I found a deal but not sure how to find out more juicy details, for instance:

1)environmental problem ( from the city ? )
2)gov't lien, tax lien (county recorder office ?)
3)complaints by neighbor, passerby, etc ( ?? )
4)billboard (basically the building has a billboard but i m not sure how to verify whether the contract is existing, expired, and any pertaining problems)
5)how to find the current market rate of per sq. ft for lease ?
6)anything else I should start researching ?

thanks for your help