First of all, try to pick your helper carefully, this isn't as important for this effect as many others but it's always a good idea. If you only have a spec who is obviously intent on busting you then this probably isn't something you should do for them, at least until you get some performances of it under your belt and have built up some confidence.
The important thing is to use your best acting skills and always try and appear natural and unconcerned. If you broadcast any fear or worries (even unconsciously) your spec will pick up on that become much more suspicious of everything you do.

To answer your specific questions...as long as you don't appear to be looking for any marks your spec won't either and therefore will never "see" anything.
The same is true for any "moves". If you act natural they will go by unnoticed. Or you can present it as a do as I do.
Remember to tell them why you aren't going to look at the cards and don't want them to either. It makes sense and is perfectly logical and unless their goal is to bust you they will simply follow your directions.

So the key with so many of these types of effects is for you to erase any worry from your mind because if you seem worried then they will too.