With the eldar, on any given map, I infiltrate my base as soon as possible.
Don't. It takes a fair amount of Req better used on other things at an early stage. Make use of every unit you can get your hands on first, then worry about infiltrating your base. Firstly you want to have most of your base up and running, taking as many SP's as possible in that time. At the earliest, wait until you have your 3rd Tier research going to do that. Worry about putting Gates next to each and every SP up until then. I also like to put the odd Aspect Portal next to the out of the way SP's, the ones that the enemy ignores. You should also set a gate or two up near the enemy Base, but somewhere secluded, you can use them for Hit and Run attacks and when the final charge is ready, as a staging point for the attack. Try to attack from two directions at once, A large force of harrasment and CC 'Tie-Up' units to draw the enemy out and then a second force consisting mostly of anti armor/building weaponry to raze their base while they are distracted.
Harrasment/Tie Up Units:
Wraith Lord x 2
Fire Prism x2
Seer Council w/Farseer
Fire Dragons w/Falcon x2
The general idea is to tie up the enemy out of their base, the Seer Coucil/Farseer and Banshee's and Wriath Lords will keep them locked in combat, the Fire Prisms add heavy weapons for Mech killing and also disrupt Infantry, the Wraith Lord can do this also if needs be.
When thats going , bring in your second force and let them loose on the base, set their stance to Burn so they will target buildings first.
I build webway gates next to every point I take, I also build them in random far away places.
I build two squads of guardians to take points. I max bone singers and get the farseer asap, followed by infiltrated scouts, dark reapers and fire dragons.
I don't often use Ranger squads, their infiltrate ability is pretty useless against a savvy opponent, and because they know you are using Eldar, they will be expecting alot of that ability and plan for it. On Infantry its only a short term benefit, but can be used to take SP's ,CL's and Relic's from an unsuspecting opponent.
Reapers are good, their range is their strength but power is limited by opponent. You will have to judge what unit is best to use depending on the opponent. Fire Dragons should NEVER footslog, they are too fragile. Stick them in a Falcon with Plasma weaponry upgrades, this way it can point defense its cargo and also help when attacking a base.
I build up to 15 on the squad cap. I keep the entire force in the webway gates. I teleport round, annoying armies and defending my base. I max wraithlords and wander about. As soon as I can buid the avatar I do (why I only normally go to 15 on the squad cap for a while). Then I get fire prisms and the seer council for the farseer.
Then I normally wander off and try to take over the world.
Sounds about right, but you seem to be turtling your forces, you need to be attacking them all the time, stopping them from amassing forces. Just sitting there will give them plenty of time to get out a sizable force and their best units.
Thats about it right now, i'm at work and a little busy. I'll speak more on it later if you need any clarification
As for your PC, unless its running W98, you should be fine playing online. In all honesty, few people leave the Graphics settings turned up during online matches as it can screw with their connection among other things. Unit Occlusion is a must but otherwise leave it all medium - low settings. Oh, and turn Persistant Bodies OFF.