Last year, I made the leap of faith of using a bivy and poncho tarp- forgoing my tarptent.
I backpack in the Sierras and the San Francisco Bay Area.
I would highly recommend that you consider getting a bivy, which will give you some protection from rain splashes or rain being possibly blown into your tarp.
The bivy also affords me a little more warmth in my sleeping system....optomistically up to 5 degrees F more.
A bivy with a built in head net will keep the bugs and critters out while letting the moisture from your exhaling to easily vent out and keep the condensation in the bivy at a minimum to non-existant.
I admit that it took some getting used to sleeping within a bivy bag, but on the plus side, I have really enjoyed the 360 view from under the tarp, which I did not have in a tent.
I feel more connected with the environment that I am in.
I even recall a few nights where I was laying in my bivy watching the full moon rise and being able to see it all, where I could not easily do so in a tent.
Furthermore, I have even had a number of nights this year where I slept with the bivy open and I survived!
I did have a few bugs, spiders in my bivy, but I guess I did not smell good because I have not been bitten by anything yet.
Never had any small or large animals molesting me either.
In my yellow bivy, I look like a giant Twinky to an bears out there. :)
As for fear, if you hike 20 miles a day....you will be too tired to wake up if something visits you at night, so you will either get a great night sleep or you will never know what killed you.
It is all good!
P.S. Regaring a bivy....carefully look at the thickness of your sleeping pad and the loft of your sleeping bag. In some cases, you might opt for a wide version of a bivy, which I have....gives me tons of room inside without crushing the loft of my sleeping bag.