My experience with powder coating is that it lasts better than an aerosol paint job.
North Shore Powder Coating at Artarmon did my last coating job. The guy that ran the business then (2007) has sold the business on. I haven't heard any bad reports about the new owner, but it is worth checking out some of local car tuner forums for other suggestions.
Mind you, if you want to just get the job done, it's very easy to give the door handle, mirror and quarter window pillar a quick paint with satin black.
Something I did notice on some of my door handles is that the lock cylinders had cut into the base casting, as illustrated in the following pic.
Regards,
Owen
ps. I am curious to learn more about the key-less entry system you are planning to install.