beginner's theory lesson

First thing and easiest thing to learn is that each one of your fingers has it's own number: The thumb is always number 1, the index finger on either hand is 2, your third finger is 3, your ring fingers are 4 and the pinky is 5.

Musical notes are written on a set of five horizontal lines called a staff. In piano music there is 2 staff, they are then called staves. Notes can be written on the lines and in the spaces between the lines. Each note name has a different position on the staff and these note names are actually letters of the alphabet from a-g and starting again at a and so on...

With piano music, the top staff is for the right hand and the bottom staff is for the left hand. The 2 staves are joined with a bracket so you know you're supposed to play both hands at the same time.
When you see numbers above or under notes, they are usually the number finger you're supposed to play that note with.

Music also tells you how long to make each note last. The beats are figured out from a fraction point of view. Imagine a whole pizza being the whole note, you cut it in 4 pieces hence it's 4 beats. If you'd cut the whole note in half, hence the half note counting 2 beats, how about using a quarter of the whole note, hence the quarter note lasting one beat. Music is math!
It can take some time to relate written notes to the keys on your piano but the more you look at music sheet and try to play it, the easier it will get over times.

You'll eventually learn about silences, these signs tells you there are no notes to be played for a certain amount of time, for example the quarter rest is quiet for the time of a quarter note, the half rest is quiet for the time of a half note and so forth....it's pretty straight forward really.
If you have the choices of a few piano teachers around town, I'd probably go for one that you feel easy going and comfortable with. If a teacher has a difficult schedule that doesnt meet yours but has great credentials; I'd say keep on looking because it's actually not important to choose one with great credentials when you need to start with the basics, any teacher will know the basics so pick one that fits your schedule and you get along fine with. If you pursue your studies to the point where you need someone that can teach higher grades, then of course you'll have to shop some more for a more qualified teacher but you'll also pay more... The higher a teacher has gotten in terms of degrees and grades the more she or he is apt to charge.

Good luck and have fun!