The tachyon device will likely make time travel easier for Reverse Flash given that it takes a major amount of speed and the speed force to hit time warp speeds.
Also given that this is time travel, it is possible that teh RF that beat up Wells was a future version of RF/Wells from AFTER the tachyon device was stolen, and Wells/RF had to go back to fulfill that part of his plan.
Also we can likely expect both RF and Flash to go back to the night of his mother's murder. It will be Flash that saves young Barry that night and RF will still kill his mother.
As to why Wells/PRofessor Zoom/Reverse Flash doesn't just kill Barry, Iris, Joe, etc., he is bound to the future history as Barry is supposed to be. he cannot just kill them as that would create a paradox of unknown ramifications. RF is apparently out to ensure Barry becomes a hero, assists him as Wells and then as Reverse Flash torments Flash and constantly gets him to push his powers and skills, thus making him a better hero that can face the future Crisis.
Why is Reverse Flash doing this? Simple, he has to or he himself will likely not exist. He is trying to preserve the future as he knows it and also his own existence, which again is why he cannot kill Detective Eddie Thawne and may have to actively protect him at times.
Also, why he is doing this is simple: a hero needs a villain, and the Reverse Flash is likely Barry's greates foe.
Also, What is that future Crisis event yet to come?
is it like COIE was, as barry will need to become fully flash fast, in order to die so that all others cam live?
maybe Zoom really needs to [repare and train barry to become fully Flash, in order to avert the crisis?