Enlargingcloud makes some good points, but I have some of my own I would like to add.
I don't feel that you need to make a great deal of changes to this list, but there are one or two areas which would benefit from alterations.
Enlargingcloud dealt with the Conceal issue on the Warlocks, so I'll just say that I agree with that and move on.
My concern centres on your infantry/mechanised balance, which I feel is too strongly skewed in favour of the mechanised wing. In my experience, you need a counter assault/defensive assault unit on foot to protect Guardians, or else a clever opponent will just dodge your mechanised wing, smash through your Guardians and spoil your entire strategy.
I would, therefore, drop the Harlequins and one of the Falcons (if you were using the Harlequin/Falcon combination in fourth edition, that was not in line with Eldar background, so I wouldn't have recommended it then, and I still don't recommend it now), and take a unit of Striking Scorpions on foot and deploy them with the Guardians.
If you are going to use the Fire Dragons in a multi-purpose role, then I would be tempted to add a couple of models if you can, otherwise it may just be better to run them purely as an anti-tank/elite MEQ unit, and drop the Exarch.
Eldar transports don't need Vectored Engines any more in my opinion, since the damage to passengers if their skimmer is shot down while moving flat out is very insignificant most of the time.
Given that you have no significant firebase, I'm not convinced that Pathfinders are really going to help you that much. I feel that the points would be better spent on a scoring unit for the mechanised wing (see below), so you could drop this unit.
Using the saved points, I would be very tempted to add a unit of Dire Avengers in a Wave Serpent to the mechanised wing, since I have found that it's important to take a scoring unit in a mechanised wing, as you can end up destroying the opposing flank, but then having no squad available to capture an objective on that flank, which can cost you victory.
To answer your three questions:
a. Three scoring units can be sufficient in a 1500 point game in my view, but one of them needs to be in the mechanised wing (see above comments).
b. Harlequins can still work in close combat, but they are at their best against high toughness targets, so really are not needed against regular armies, especially if background plays a part in your thinking too. Their biggest problem comes from reprisals, as not being able to consolidate into combat any more causes them severe survivability issues.
c. I'm not quite sure I really know what you are trying to say here, but assuming you mean are Jetbikes harder to hide behind cover than before, the answer is, generally, yes.
d. The Autarch works in the same way as before. The way the missions work, however, has changed somewhat. I don't have my rulebook with me here, and quoting from it isn't allowed anyway, so I can't give you much information on how this works.
Tactically, however, I wouldn't start this army in reserve, since you have a mixed force, and mechanised forces are those which are better suited to the reserves strategy.
I'm sorry for being a bit vague here, but the problem of living in two places, is that I don't always have the relevant books to hand, and because I don't ever use an Autarch, I don't tend to think about the reserves rule very much
There are some other changes I could suggest to your list, but in light of your remarks about lack of cash to spend, I have decided to keep suggestion for unit alterations to a minimum, especially since the list is fairly solid in most areas in my view.
I hope that helps.