Need assistance building a 500 point Sinestro corps team. Can only use pieces from WOL set. I have all the figures, Parallax, all the constructs, the battery, and the ring.

Lyssa drak, weaponer of qward, 160pt sinestro, yellow battery with the constructs you think work best to your playstyle. Seems like a fun enough team.

I'm sorry I'm replying weeks later, but as a player of a lot of Sinestro Corps teams, here is my advice...
The most important figure to use on your force will be the full (250-point) Sinestro and an all-Yellow Sinestro Corps power battery. Given Sinestro +1 to his combat values, and supporting him with the Yellow Emotional Spectrum effect is quite strong. I typically assign Sinestro either the Decoy (Shape Change for 6 points) or the Bulldozer (Force Blast for 4 points). My experience has been that if you want to support him with either the Net (to further reduce opponent's attack values) or the Wall, just assign those to another character on the force.

This maxed-out Sinestro is a very effective one-man-army, especially when supported by fodder. Sinestro is all about sacrificing his minions while being brutal all by himself. Almost any force you build top support him should be effective. Here is one suggestion:

250 Sinestro
2x50 Sinestro Corps Recruits
77 Romat-Ru (early TK to set up/retreat from alpha-strikes)
30 Despotellis (highly annoying figure for most opponents)

6 Battery + Ring
8 Net (<- Special Hindering terrain is effective)
8 Stop Sign (<- great against HSS)
6 Decoy (<- best "passive" defense for a one-man-army)
6 Spotlight (<- This is my last choice, YMMV)
4 Bulldozer (<-knockback is a great side-effect for an attacker)

= 499 points

I'm a big fan of the Karu-Sil piece, but at 500-points I think she's too costly to support Sinestro... especially when you can get two other characters for approximately her cost.

Notes about Parallax:

At 250-points, this is not a bad choice to serve as a tentpole instead of Sinestro. You lose the opening move and attack, and you have to be used to playing double-based giants. If you go this route, depending on the opposing team, you may want an ally ready to drop smoke clouds (from the Net) right away to put Parallax in hindering terrain (most WoL factions are focused on range, but many will have their own Spotlight). The late-dial 'grip of fear' can be very nasty against opposing teams if they are piling on against Parallax.

I have never used Parallax as the OMA because I find Sinestro to be much more fun!

As a possessing 25-point entity: First, remember that you can use Parallax to 'recruit' any other WoL figure into the Sinestro Corps if that is the way you roll, so you aren't strictly stuck with only figures that have the keyword by themselves. The best use of Parallax (w/ Yellow Battery) is to bring an already tough/annoying figure with a long dial but without the keyword onto the force (think Sayd).

Because Parallax starts with Quintessence, using him as a possessor for Sinestro isn't a bad idea, and there is some possible synchronicity late-dial... but if you end up with a late dial Sinestro things are probably going pear-shaped!

Other characters to consider: I've never used the 300-point Superboy Prime as the tentpole for such a team. He may be a better choice for Parallax possession because of the way the dials align. The Kyle Rayner and Hal Jordan corps members have Quintessence on their dial so possession is not an important consideration for them. I like Kyle's trait to further reduce attack values if you lose map choice. I've played against these figures and have beaten them so I am negatively biased towards them. YMMV. The Weaponer is a strong dial, but it can only take out one opposing figure at a time, and it has very limited mobility after an alpha strike.

Finally, if you are playing against other WoL figures, the will have lots of tricks in their arsenal (Perplex, Outwit, PC, other Constructs). Make sure your OMA has the help of his buddies to deal with them.