500 points is a hard game sometimes with more elite forces.
Personally I'd take a cheap farseer over the aurtarch. The farseer has the advantage of a wichblade against tanks, and can be given a power whilst still remaining playable at those points levels.
10 man dire avenger squads might be a touch of all your eggs in one basket. Your dealing with around 170 points. They have a limited shooting range, and can be taken out with a single pie plate. I'd opt for 2 5 man squads so you can split targets. costing 60 points a unit.
warwalkers would be a great asset in this points size. High refire rate, and cheap with scatter lasers or shurican cannons.
Rangers have never done well for me. That's a personal issue i have with them I tend to play mech eldar, and there style leaves them stranded to get flanked. If you have a more static army then there a great addition. But typically for eldar you have to work in either a gun line force, or a mobile force, Mixing things up at low points will leave the army open to vulnerabilities.
A great addition in low points gunline army is a Wraithlord. Scatter laser EML, dual flamers, and keep a farseer nearby to babysit.
To get the most out of the bikes and a fast force, think about adding the farseer, a single power (fortune), and the bike. It will pump his cost a little, But you get the advantage of the rerollable cover save/armour save, some armour destroying with the wichblade, and some shooting with the catapults/cannon.