If you want to test your maxes try testing out a weight you think you can handle for 5 reps. You can then plug the results into an online calculator to give you an idea of what your max is. There is a calc on bodybuilding.com, it will probably be a little high so if you want to work at 80% max I would actually start at 70% and work up from there.
I think it is a really good idea to get at least a clue as to where your strength is so you can plan your workouts intelligently.
8 reps is nice middle ground, my workouts generally work in rep ranges from 3-12. Occasionally I will go higher but its rare.
You really just need a simple routine, and make sure you dont overdo it and jump in too fast. That just leads to injuries or being too sore to keep up with it.