Since this project seems to be your baby, this should not be the first project you attempt to write using PHP. You will kill your baby if you do that.
Learn PHP by creating a couple other websites first, maybe that have similar characteristics as your baby.
If you want to hire, ask for references and actually check them. Ask the references if the developer or firm met the deadlines, delivered what was promised, and didn't demand more money in the middle of the project. Evaluate prospective developers by how much effort they go to in the bidding process. If you see a detailed function list with estimated hours next to each item on the list, that's a good sign. A one-sentence bid "we will do your job for $xxx" is a good sign-- to run away.
And just a personal opinion, work with someone located in the same geographic region as you. Time zone differences and/or language barriers can be extremetly frustrating.