First off, for something like this, it will be very handy to have a service manual or a subscription to techinfo.subaru.com, as you will know all the information is correct from there. It will be the best referance you'll have handy.
If you are not confident at all, I suggest you find a friend or someone local in the area to help your or has experience in doing something like this. Paying a bit more is better than bending valves, although the procedure can be very straight-forward.
I haven't done DOHC's for a while so if someone smart notices an error please do correct.
Driver's side will be under load upon aligning the marks. The cam sprockets as I recall only go on one way if you remove them.
My rule of thumb is always have the sprockets unload (unless you are just doing a timing belt) and upon realigning the marks, find out which direction (Clockwise or counter-clockwise) will be shortest upon the cam lobe hitting the valves. Turn the cam sprocket with a 17mm to that shortest distance. Repeat for the bottom.
You should not get any interferance if you did everything right, but if you do feel interferance between the exhaust and intake valves, work your way around it unloading one and loading back the other.
After putting the belt and tensioner on, manually crank it both left and right to hear or see anything weird in both directions. Line everything back up one more time to check all your marks and make sure they are where they are suppose to be.