With the Silver Surfer is it 'legal' to move normally, then attack normally, then escape up to 5 spaces using Hyperspeed?
That's what the Hyper Speed 5 ability says it does: lets you move 5 spaces after taking your turn.
If allowed, then presumably he is liable for leaving attacks.
I don't see why he would take leaving attacks. His Stealth Flying ability reads to me as if it applies whenever he moves, and Hyper Speed 5 lets him move.
Whilst under the Stealth Flying it states that he does not suffer leaving attacks if engaged, this would be use of another special power.
I see nothing in the rules about two special abilities not being able to apply to the same action (except for the bit where you have to choose between making a normal attack and using one of your special attacks, which isn't germane here).