I would probably suggest a smaller tarp as well. If you try to hang from trees that far apart it will be really frustrating. For trying things out you could even consider a cheap poly tarp from Wally World for only a few bucks. Noisy and heavy but you can always use it to cover the lawnmower later when you get something lighter. I have personally never slept in a store bought hammock...had an ENO double for a while but didn't like it any better than my homemade. It was great quality though. Was able to sell it here in a few hours when I decided to so even in the unlikely event you don't like hanging you could recoup much of your spending with a name brand.
Homemade hammock is one of the easiest projects ever. Check out Jeff's http://www.tothewoods.net/ and Risk's http://www.imrisk.com/ sites. I tried one of Risk's test hammocks first for about $12.00. I build Risk's zHammocks as ther are great for pad control. It doesn't hurt to have the double bottom for security as I am big and heavy. Bugnet easy to build as well. Go to the SEHHA campout if you can...even if only for the day on Saturday. More info there than you can imagine and seeing one of Ed's hammocks will show you how easy is is to build. While there you could probably pick up Ed's book too. Required reading in my opinion...my copy is almost worn out!
You have found the most complete source for hammocking on the web and a great bunch of folks to boot.
Finally...get ready for the best camping sleep ever!