How hard is it? Well that all depends on what level of knowledge you are at before you start. If you've never flown a study sim before, and don't have any knowledge of military aviation the answer I suspect is very.
DCS and LOMAC are very different sims, LOMAC is a low fidelity survey sim and is primarily about throwing planes around the sky and having fun in a somewhat less than realistic way (basically airquake for the most part).
The DCS series are study sims, as the name suggests in order to play them, you have to study. If as is appears you've never flown a study sim, yes there will be a very steep learning curve. Now the questions you have to ask yourself is are you genuinely interested in learning how to fly a military attack helicopter? Because that's what you'll be doing to all intents and purposes, obviously you don't HAVE to fly using real life procedures and check lists but it is half the fun
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Half of the fun for those of us who enjoy study sims is the learning process, I flew Black Shark for around 4 weeks before I even loaded a weapon on to the aircraft, let alone fired one, that's not to say you'd have to do the same. I'd say that starting with minimal knowledge, it'd take you a couple of weeks (assuming at least 2-3 hours a day) to be able to fly a combat mission and not die in seconds).
As for controls, NO you cannot fly with a keyboard. You really do need at least a basic stick, but a full HOTAS + pedals + track IR is the best way. Of course this is expensive, but the thing you need to know about study sims is that if you get into them, it is expensive and time consuming but the rewards are more than worth the effort.
For example, back in 1998 I spent £30 on a sim called Falcon 4.0, nearly 12 years later I still fly it and it's still one of (if not the) the best study flight sims ever, £30 for 12 years of enjoyment find me an FPS etc that offers that value for money.
One thing to remember is that the flight sim community is the most helpful and accommodating of any gaming community, and is always willing to provide help to a newbie. Many people will even be happy to connect in multiplayer and provide some one on one training if that's what you want.
Just remember, study sims are like a heroin, once you start it's almost impossible to stop.
Of course, you could buy it and then fly it in arcade mode, but if you want to do that I'd advise you save your money and go and buy HAWX or a similar arcade game.
, but I thought force feedback was used on compliant joysticks to actually make them harder to operate, for example, if doing a nose dive in a jet, trying to pull the nose up would be physically harder then if at level flight?