-why would Ford have Bernard (potentially) kill Elsie? wasn't she helping Bernard to stop their data from being taken out of the park? (which is what theresa and charlotte were trying to do)
Don't think she's killed yet, and think she was taking her out primarily because Ford had some sort of inkling as to what was happening with the data transfers and didn't want a wrench thrown into his plans, even if that monkey wrench was to stop the espionage.
-was the scene where delores kills bernard simply bernard going mad because of his ability to remember past experiences?
She didn't kill Bernard, she killed Arnold, and only at his behest as he thought the massacre would only stop the park's opening if a real person died as well.
-is the generally accepted theory that Ford's (actual) new storyline was to recode Delores, Maive, Bernard, etc to take over the park?
Sort of? He has a "storyline" to present to the board (as seen with all the guests at the end) but yeah, his end game was finishing the Reverie programming that Arnold started and which would've given the hosts sentiency.
-maybe i missed what Billy said to Logan before sending him on the horse at the end, but did he end up taking control of Logan's family's company and bought majority of WestWorld?
Yep. It was vague how he wrested control out of Logan's hands, but assumedly sending him off naked on a horse played a factor - either in proving Logan to be unstable or possibly even killing him.