Schepp himself wrote:My greatest fear is that my shooty platform is not powerful enough to overcome a real shooty army and then my counterstrike units have to take out some squishy shooty units of the enemy.
I have no experience with this and am struggling how much points I have to dedicate to this part of the army. I'm thinking mainly of lootas, devestators, tau suits or similar units.
In any game, you have to decide on the field which enemy units pose the most threat to you winning and you have to deal with them. Now the two important things here are "you winning" which is not the same as having your units survive and "deal with them" which is not the same as killing them. If you can move your army in such a way that lootas or devistators can't draw line of sight to anything in range and they have to spend several turns moving to get into a position to fire, you have delt with them. As for winning, in a 2 objective game, you can have a lone trooper model on your objective and his transport on the enemy objective with the rest of your army totally destroyed and not a single enemy unit dead and win so long as there isn't anyone contesting your objective. These are really the things you have to think about more than "can I kill my opponent's army". So to this end, what does a combined arms approach provide you in terms of winning. Well in objective missions it means that you have half an army to sit back and defend rear objectives while the other half can move forward to capture / contest forward objectives. In kill point missions, it means that you have a lot of options with which to go about killing your opponent and keeping your own units alive.
So, the good the bad and the ugly. Against armies that sit back and shoot, you will do decently. Your shooty units should be able to trade shots with them to reasonable affect while your fast units zoom up on them. At this point your opponent can either try to cripple your fire base or down the assault units bearing down on him. Either way, you still have very dangerous units pointing at him. Just make sure that in the first couple of rounds, you focus your fire on the elements of his army that pose the most threat to your skimmers. As long as they are alive and dangerous, he can't really ignore them.
Against armies that all charge you, you are in a very good position. All assault armies have to get to you before they can do much. This puts you in a doubly good position. First off, you can pepper them with shots on the way in and really blunt their force. Second, with eldar mobility, you can set things up to fight on your terms. Move backwards as necessary and set things up so that your close range units are the ones that get to open fire first (as opposed to the enemy units) or charge first, depending on what you're fielding. The trick here is that you have to be patient and let them come to you, don't meet them half way. The more time you get to whittle their forces down, the more likely you are to win. The other option here is that if their whole army is comming across the board, you can zoom over their heads in a skimmer and go harass their back field. If there is anything back there, it's going to be weak to hand to hand units. If there isn't anything back there, you can capture objectives unharassed.
Against mixed armies like your own, you are on even footing. In this case you can play the dancing game of trying to dodge around eachother and sacrifice pawns to bring valuable enemy units out into the open. It is in fights like these that you really have to think though what you are doing and how best to use your troops.
The place where you will find yourself struggling is against gimic armies. Nob biker armies, green tide, land raider spam and 3 monolith armies will all give you trouble due to their overload on one aspect or another. The combined arms eldar army tends to be a good generalist army and doesn't do so well with armies that require lots of one type of specialist to deal with.
All in all though, I would invest a bit more in your forward units than your rear units. The rear units provide fire support for the ones in front and deal with any outflankers or deep strikers that show up, but do not need the force of numbers investment that really pays off on the front lines. I would say a 60%-40% split should serve you well.