Buying a new minivan

I don’t know where to start or who to trust. I want to do 99% of the transaction online. I want to do all my research, contact the dealership with model I want, test drive, sign papers and leave with car. I get the creeps thinking about shopping around. I’ve gone on many websites but none of the info seems to match up. Please advise me. I’ve had sales persons dive into my car as I’ve tried to leave. I want a simple, quick, painless and non-pressure transaction. A question I do have before I start, 2004 Chevy Malibu in excellent condition, do I sell or use as a trade in? If I should sell, where should I do that. Thanks all from a green around the gills girl.