1) Don't discount ancient gear. lots of old stuff (like old external frame packs) are perfectly good. A backpack doesn't
have a best before date.

2) If you really want to lighten your load up, start with a look at the "27 pound 7 day pack" and the 18 pound 3 day pack" list posted on the main site this forum is on. Some of us also post gear list that are semi lightweight.

3) Rather than worrying about how heavy your gear is at first, concentrate on what you are taking and *not* taking. look at what some of us are taking and think seriously about what you would use for the same purpose. You may find that, ok, you don't end up with an 18 pound pack for a weekender, but by carefully planning what you're gonna take you may end up without a huge heavy load either.

Once you've gotten there. you can start thinking about what you may want to change to lighten up more.

As for tarps, there's lots of ways to deal with bugs, everything from a headnet, a net-tent, or a hammock with a bugnet. You could also look into something like a tarptent from TarpTent or Six Moon Designs.