I post more over on tacomaworld, but check in on here every now and again.
If you want to regear, I second not going any higher than 4.10. Maybe even 3.73's from a v6 taco. But I would regear if running 31" tires. FYI, the 4cyl prerunners come with 31" (245/75/16) tires and they run 4.10 gears.
As far as traction help an ARB air locker is probably the more expensive, but probably the most highly regarded locker out there for tacomas. You could also go with a lunchbox locker like a powertrax no slip or, if you want an LSD, the detroit truetrac or Eaton LSD. The 6 lug E-locker has a smaller ring gear and has been prone to failure on some trucks that get wheeled hard. Also, it won't fit in the 8.4 axle housing. The elocker third member has a different bolt pattern, so unless you want to fab something up, it won't work easily.
If you want to find out more about the tacoma gears check out http://gearinstalls.com/
for lots of great info, especially if you are planning on doing it yourself