best bang for the buck is gears, 3.73s or 4.10s. As far as timing goes, you can get a mechanical timing adjuster, but the more popular choice is a handheld tuner, that will also allow you to upload custom tunes, select gear ratio, tire size, fuel at WOT, read and clear trouble codes and a bunch of other neat stuff. Tuners come in handy as the mod list grows.
You can run an o/r H/X or one with cats, its up to you. One big PITA is longtube headers. They provide good power gains but are a time consuming, involved install process.
First thing I would do would be gears, and O/R mid-pipe, and maybe a shifter.