I think it's likely that Bateman was dealing with major psychosis but did not genuinely kill anyone, including Paul Allen.

In the hookers scene, we see Bateman walk about the living room while speaking to the hookers. They sit on a white love-seat, he sits on a black, armless love-seat. Across from Bateman is a metal, backless, armless, double-seat. There is a small end-table and a glass coffee table.

In Paul Allen's Death; Bateman moved his furniture around and covered it. Allen sits in a SINGLE-SEAT with a back, next to him is a Single, Backless seat. Far across is a Table, to the side is the White Love-Seat, and in the corner is, what appears to be, a Chaise Lounge (The seat psychs have you lay in, traditionally). The telescope is also missing. He also wields an axe with a mirror finish, which just isnt a thing you normally can find, new axe edges may be mirrored but the heft of metal is normally either matte or painted.

When his secretary comes over for their date, the furniture in the Hookers Scene has returned.

My theory is that he imagined killing Paul Allen, with an axe that he aggrandized as being posh; while in reality he smashed one of the seats of his Black Love-Seat, one of his armless seats, the end table, and the telescope: Which one could easily imagine he likely made into an effigy of Paul; two seats on the floor for his torso, the end table as his legs, and the telescope as his arms/head. He then placed the heap of rubble into the bag he is later caught with; which also explains why he has the ability to fit "Paul" into the bag, as well as carry it downstairs and to the vehicle - it's probably 100ish pounds of scrap.

- The Chaise Lounge is the tell that he is imagining this, as not only is it used for therapy; it's also never in his apartment any other time. This piece of furniture was a subconcious tell that the scene was a delusion.With Paul Allen's Death being questioned - it would stand to reason that the other deaths are delusions as well. He likely DID beat the hookers, but it's unlikely that he killed them; he certainly didn't drop a damn chainsaw on the one girl and kill her - not to mention that it's awfully coincidental that he was watching Texas Chainsaw Massacre and he is suddenly a Chainsaw Sharpshooter. He beat a homeless man and his dog to death, yet didn't have blood all over himself. The ATM told him to feed it a cat. He blew up a car. These are all movie references:

Chainsaw Hooker Death: Texas Chainsaw MassacreAxe-Wielding, Raincoat Wearing, Killer of Sinners: Jason Vorhees - Axe-Wielding, Jumpsuit WearingFeeding a Creature for Monetary Gain: Seymour Feeds Audrey 2 for Fame (Little Shop of Horrors)Blowing up a Car: Basically any action movie, ever. Possibly Terminator; since he's a Horror-FanKilling a Homeless Guy/Dog: Many Horrors start with a nobody being off'd. Possibly a reference to The Thing '87, as "The Thing" first infests a dog.

This would also explain why he didn't Kill his secretary. Originally, he intended to duct tape her and torture her - A la B.T.K.; however, when he mentioned Ted Bundy, she replied, "Who's Ted Bundy?" which ruined his fantasy. Moments prior to him shooting her in the head with a nail gun (My Bloody Valentine, 1981) he mentions he was "Looking for a meaningful relationship with someone special" when the phone suddenly rings. This forces him to set his nail gun down - as it ruined the moment, once again. The only legitimate kill in this movie was this kill - Bateman really WAS going to kill Jean, as he had a long history with her in a positive light and he had chosen her as his first true target, "That someone special". However, when snapped out of the moment, he came to his senses and asked that she leave so as to spare her.

TL;DR: Patrick never killed anyone - he was hallucinating delusions that were fueled by all the Horror-Movies he had watched. He attempted, only once, to genuinely live out this fantasy when he attempted to kill his secretary, Jean, in a manner similar to the BTK killer, then similar to a scene in "My Bloody Valentine (1981)", however, both situations fizzled by the fantasy not living up to reality, so he spared her. There's a therapist's couch in his apartment that is seen only once, during Paul Allen's Death, that is our tell that he's delusional.