Your 4runner will do just fine, in fact it will probably surprise you just how well it appears to take on what may seem like challenging terrain to you.
First time I ever went wheeling i was pretty nervous and stopped and poked a stick into every puddle on the track to see how deep it was, but after many years of experience i often find myself accellerating into them now! (Dont do that, its bad for the environment and your car)
Read the 'sticky' article on off roading tips at the top of this sub-forum. It is very good and will help you alot.
Have fun!
Being that its your first time out, the 4Runner will probably do fine on whatever you want it to, just use common sense. they're very capable, just don't think your on an ATV (ive been in a few tight situations)
Have fun but be careful. My last time out I came very close (like an inch) to rolling over sideways on an embankment after I went airborne - see my sig pic
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2005 Pacific Blue Metallic SR5 4x4
2003 Dorado Gold Pearl GX470 (2003 Four Wheeler & 4x4 of the Year)
2000 Millennium Silver Metallic SR5 4x4 5spd - RIP