I sleep in a full tent myself - but have researched and built tarps in prep...

Most people use a ground cloth of some sort in tarp shelters. Simple piece of plastic sheeting like this works. A lot of people use Tyvek home wrap - I bought a roll from Home Depot. You can fold up the corners and make a semi- bathtub floor for extra protection.
You'll also want a sleeping pad. This is another layer vs. moisture and also warmth + comfort. Closed foam is classic, but as a side sleeper I love my inflatable pad (therm-a-rest neo air).

Bugs are just a downside of tarp shelters. A head net is one option. Or a bivy with bug protection. Another thing it sounds like you've already considered is a net to sew/attach to your tarp and drape down. It basically hangs from the edges and creates an enclosed area against flying bugs.

Not sure about animals.... First - keep your food away from where you sleep. I hike with a dog, so most animals stay away naturally. Otherwise - just consider it part of nature, most of them are more scared of you than you are of them.

The normal suggestion is to support the tarp with your hiking poles. You can also use trees, but poles are convenient if you have them already. It takes practice getting the tension just right. Really - the whole process takes practice. Set it up in your back yard or the local park. Do it 10 times before your trip and you'll be a pro.

Here are a few good resources:
[http://sectionhiker.com/square-tarp-pitches/]9http://sectionhiker.com/square-tarp-pitches/)
http://sectionhiker.com/how-do-you-sleep-comfortably-under-a-tarp/
http://sticksblog.com/2013/06/10/setting-up-my-zpacks-hexamid-solo-plus-tarp/