I vote doable. With GE you should be okay at LAX to check out F lounge. Honestly, it's a good lounge and I do like the food there, but it's not a "must see" lounge like some at HKG (where I'd be disappointed to not get at least an hour in my way through).

With the designation of co-terminals and a stated MCT for EWR//LGA flights and the fact that AA will book co-terminal flights as a single ticket, you should be protected. However, I have a feeling they'd still have you fly out of EWR, probably on AA metal through DFW/LAX if CX doesn't have another EWR-HKG that's a better option.

i am certainly no expert though.

Fwiw I think you'll end up with the lower RDM in sept. Also, LGA-EWR isn't cheap in a cab... Friend driving you? Otherwise keep that cost in mind as well when determining value/cost.