I converted from microlights onto helicopters and had a lot of the same questions at the time. Some answers below..
Engine failure. You have x seconds to react to an engine failure. You need to pull back on the cyclic and start to lower the collective within a couple of seconds on a low inertia rotor (like the R22) or more in a higher inertia rotor (G2 or R44). You have a warner beep when Rotor RPM goes below 90% and that helps focus the mind. Practice and Practice. Engine failure in helicopters is pretty rare though so don't worry too much.
Difficulty. Learning to hover is based around how good you are at noticing very small changes in pitch/attitude and then making very small reactions on the cyclic. I had a pretty good hover sorted within 3-4 hours as was used to attitude changes from flying planes. I would expect transferring from Gyro wouldn't take you very long. The challenge with helicopters is learning all the sloping ground stuff, landing in confined areas stuff, run on landings... its all good fun but there is much more than in learning to fly planes.
Hands off - Correct. If you let go of the controls the helicopter will move one way or another - its an unstable aircraft. Its perfectly comfortable to fly for 2-3 hours though hands on in a R22/44. The cyclic just naturally sits there on your lap and your hands just subconsciously do their thing making very small adjustments.
Cost - If cost is an issue don't fly helicopters. They are expensive things. You should expect to have fixed costs of $10-20k per year on insurance and hangar etc and then for a 2 seater (R22 or G2) around $250-$300 per hour for fuel and maintenance. $550 in a 4 seat R44.
Number of seats - I learned in an R22 and then did my flying in an R44. I flew with 2/3 passengers most of the time. Having the extra seats is very useful. It also comes down to overall weight/amount of fuel you can carry. In a R22 you are very weight limited but an R44 gives you a much greater scope to fully fuel up and stay within limited. Its also a nicer aircraft to fly as the extra rotor inertia makes for safer automation entry and gives a bigger margin of error on the flare, there is more power available for confined area work (vertical ins and outs) and a whole load of other benefits. Learn in a 2 seater and then decide for yourself when you have learned all the other things there are to consider.
Learning to fly helicopters is a blast... i loved every minute of it and the $20k or so cost was so worth it. Enjoy
