1. That point seems to stem from completely illogical reasoning - what on earth would imply that IEMs would be better than a full-sized. They are different enough in presentation and paradigms, that leaves a lot of this to be, quite frankly, moot. That being said - IEMs are more forward, they reside more or less confined to your head - typically. They can't move as much air, so a lot of things become scaled down, relatively. Yes, and I must stress this, it's enough of a difference that going about this in such a roundabout way makes little sense.
2/3. You might want to specify more on the actual sound and presentation you're wanting, rather than genres, before someone can chime in with a specific answer.
It seems very egotistic to quote oneself, but this situation is similar enough to the one this message was originally intended for, that it might be warranted.
That being said, you've listed out genres. That doesn't really tell us how you'd like them presented. It doesn't really tell much about how you want them to sound at all, really. It's a very vague quality, and the answers you get as a result will be extremely skewed towards the preference of one person to the other.
For example - the typical stereotype for a person who partakes in rap/hip-hop/electronic is that they would want more bass. Well, would you really want that in this case? How about the other qualities of the bass? Do you want them to be punchy and tight - or do you want them to be focused on texture?
And if you're bamboozled with using audio terms - you needn't be. Just by describing the sound the way that you can, and being specific about it, can yield better, more specific results from your audience. No need for jargon.
4. What is a lossless MP3? A lossless player I imagine was what you meant. That being said, all players have DACs built in, they have to. And to address your amp question...
5. If you seriously are looking for IEMs - I personally think there's some confusion and that you'd want to stick to headphones - you have to realize that they, along with plenty of other headphones - require little power. Not nearly enough to require an standalone amp. The whole appeal to them is to be portable and sensitive. Perhaps you'd like to mix-and-match sound signatures, as would many on the forums happen to do. But that depends on preferences, not only through the process of mixing and matching, but on whether or not one would want to do so at all. This should really be an informed decision, instead of being blindly told that you "need" something in order to make it all the better. And since you're looking towards a standalone DAP already, I'd imagien that you wouldn't require something to bypass an awful player - another more level-headed incentive for getting a separate ampl.
And all in all - I would encourage you to read this - http://www.head-fi.org/t/374155/leaving-portable-hifi-its-too-silly
Don't take the message too far though.