Hey Peterpan,
No great advantage by a pro except experience, training and better equipment which usually means better quality but not always I'm afraid. Remember a cured powder coat finish is a non porous plastic coating, you can damage it and it won't last forever.
Powder used to be only available in 50lb boxes or more but now new batch type equipment, custom colors and the need for quick color changes created new types of equipment that gives the home Joe a chance to play. You can buy powder now in 1lb bags or sample packs of almost any color or texture. The smaller equipment works ok for hobby projects. Don't use the house oven! The residues from the powder will contaminate your home oven. A small house oven will work fine for small stuff just don't get confused and coat your food or eat you parts. Theres a bit more to it than just getting a used house oven. It'll be a costly hobby to set up so after you coat every thing in your house and yard maybe you can coat all your neighbor's stuff too for some cash. Cured powder is unforgiving if you make a mistake. It's difficult to remove and can sometimes cost more to remove it than it did to coat it.
Remember the quality is in the preparation. The powder finish just makes your work look pretty. Crappy prep work makes the job pretty crappy.