What to expect from a tune??

not yet wait till you get some mods

It really depends on your tuner and how aggresive you want to be.

In my experience, for a normal street tune, you want to be conservative on your A/F and timing, you don't need anything crazy. Have your tuner make you a "track only" race tune that you can run when you need it.

It varies widely by tuner, you and how well your car response to it.
Example. While I only picked up 1 rwhp on the peak. I picked up 9rwhp under the peak and 10ftlbs of torque across the board. Throttle reponse is tons better, but I had my tuner put a very conserative tune on my car. My reasons were that in my area we get the oxygenated fuel, I've noticed less performance and less mpg with it compared to fuel I get elsewhere.
I've heard and know people that have picked up 30rwhp with a tune on a very lightly modded car, so you never know.