Do brakes provide full power when used from the hoods? I have been riding mountain bikes for over 20 years and am just going back to a road bike. I find the modern bars and hoods and combined levers a very strange position. I have actually loosened them and pushed levers further down bars to be more like a 60s or 70s brake position and redone the tape. I think perhaps I should have not done this and just got used to the modern position.

However, I am worried about braking. I was going down to the drop position to use the brakes and found this uncomfortable and a stretch. But I see some people use them with their hands on the hoods. Can you get full brake power in this position? Is it safe enough for going down big hills?
most mid level and up brakes / levers will offer 75% or better power from the hoods. Max brake power from the drops. 

The handle bar position is critical on long rides to offer 3 or so different hand positions. Start with the hoods level, to just above level and move around from there. I tend to micro adjust them as i get comfortable on a new bike. Seat height, frame size, stem length all play a factor in finding that sweat spot.