TJ,
Perhaps I can help a bit.
Approach air speed will be around 150 knots. Actual 'trap speed', when the aircraft engages the arresting wires, will be reduced by the Wind Over Deck (WOD) generated by the carrier's speed through the water. I believe, (but am happy to be corrected) that maximum 'trap speed' is around 150 knots, but that they usually aim for around 130 to reduce wear and tear on the wires. I could be wrong on the figures here though.
Yes, deceleration distance is around 100 metres.
Forces - that's where i have to admit lack of detailed knowledge - these will depend on the time/distance/ force schedule of the arresting engines (the large hydraulic engines below decks that allow the arresting wires to pay out, all the while applying the braking force). The scheduling of the arresting engines is adjusted not only for the type of aircraft, but (I believe) also for the weight of the aircraft as they trap. A heavier aircraft needs more force to bring it to a halt before it falls off the deck, but a less strong aircraft (say an AEW aircraft) can't sustain as much retardation force through the hook system as, say, a fighter.
Your question about heavy helmets is a good one. A the weight of helmets has increased, especially on the F-35, I am sure that the USN Navair community will have been providing very detailed guidance and instruction on how hard the aircraft can be arrested without the pilot having excessive strain placed on his neck, shoulder and upper back.
Hope this helps, best regards as ever to all those good Navair people solving those hard naval aviation issues,
Engines