A B737 flight crew reported high workload and frequency congestion on approach to LAS that led to an altitude deviation. The approach was also complicated by a wake encounter.

Narrative

While being vectored for a visual approach to Runway 19L at LAS; Controller and pilot workload was high. Approach Control frequency was so congested we were waiting our turn for check-in for roughly 30 seconds. Once on frequency; numerous 10; 20; and 40 degree heading changes were issued along with traffic calls for a helicopter and 2 737's to my left (at approximately our 10 o'clock position). I was issued a visual approach clearance to Runway 19L with a restriction to maintain 3500 FT until intercepting the Runway 19L centerline from a westerly heading. Both crewmembers were looking for called traffic but acquisition was difficult due to the numerous densely packed buildings in the line of sight to the targets. The autopilot and autothrottles were off in anticipation of a landing clearance. The helicopter traffic was again called low and close at approximately 10 o'clock position nearly coincident with a call for a 737 crossing the Runway 19L centerline in front of me for a visual for Runway 19R. While looking for traffic as I was turning left to intercept the Runway 19L centerline; I may have inadvertently descended below the 3500 ft restriction and a TCAS RA occurred. At the same time the RA alerted I saw the helicopter below me out my left window in a right turn to a northeasterly heading and passing under my aircraft. As I continued for landing the wake from the Runway 19R 737 was encountered and was evident but fortunately; not significantly disruptive. The approach continued to a normal landing following the TCAS RA. The event site location radial and distance above are approximations. The environment of Runway 19 parallel landings is particularly challenging due to the proximity of mountains and Nellis AFB. I would have preferred more spacing in a situation like this and if in a similar situation again; I will likely abort the approach. Better ATC speed control and arrival fix separation planning may help LAS better manage final Approach Controller workload in such a restrictive airspace environment. This was my first trip to LAS in nearly a year. I asked the First Officer if this congestion was common at LAS as he had been to LAS frequently in the last several months. Unfortunately; he indicated that it was.