You definitely don't need/want to combine the eVent bivy and cuben tarp. It's a one or the other thing I'm afraid. For you, I think the TarpTent is the best answer to your dilemma, and the notch the better tarp tent (for weight, shelter from elements, and 360 views free of bugs in the warmer/wetter climes. Light, full protection in any environment, and room to move around if you have to hole up. That said, if you're looking to try something less traditional ... you're not without options.
I'd pick up a lightweight bivy - probably $50 used / $80 new (Check out www.borahgear.com) AND a small tarp. You can get both for around $150 I would think. You may find it's all that you need. You may find you like a simple tarp and bivy, or you may find that you want bug protection and a floor. In any case, it's an inexpensive way to learn what you need. As to the 26 oz. bivy, I'd leave that for winter camping where you have a snow trench or cave to slide into. It seems like overkill for fair weather and confining for foul. If you like the cheap tarp and light bivy combination, upgrade to cuben fiber from Zpacks or any other maker.
Another option that I would consider is no bivy and a shaped tarp and groundsheet. An Oware pyramid or MLD trailstar might be just the ticket for you full coverage/protection, and an opportunity to hang out in rain with company if need be.