New/used has tons going on

So I just bought this pacifica touring and I'm having several issues that I was to stupid to even notice. First when the seller showed me the car the check engine light wasnt on at all, now it just turned on! Minutes after he leaves n I decided to turn off and start the car the light goes on! Also he told me that the car came with only one key which wasn't the remote starter key so everytime I try to open the car with this plain key, the car alarm goes off I don't know what to do. The reading lights inside won't go on only the headlights and back lights. I think the computer might be going crazy because the reset light goes on and when I try to lock the doors with the lock button on the drivers door the car doors won't lock only sometimes. And last when I push on the gas while not on "drive" the sound of the engine doesn't sound so good, not like your regular VROOM but like it struggle I really really need help :(