Welcome to the forum. I got here several years ago by clicking on a search for UCRs. I was looking for a better way to attach my climbing sticks to the tree for deer hunting. I had never heard of Amsteel before that fateful night. I now have over a dozen hammocks and can splice anything with a hollow braid. Be careful, this stuff can become an obsession.
As far as your height, I would start with 11' long. Longer could be more comfortable, but then you will have the trade-off of needing a longer tarp as well as needing to hang your tree straps higher to maintain the proper sag and height.
I'm 6'3" and use 10.5' or 11' hammocks. Width can help some, too. My favorite width for a netless gathered end is 64".