You should start with everything at the same time. Consider making a meal. Inexperienced chefs will start with the starters, then cook the main dish, then the side dishes, then the desert. It will be a disaster.
Experienced chefs will plan the preparation of the meal according to the cooking requirements of each dish. This means:
1. Dessert will usually be the first thing to be prepared (even though it is the last to be served).
2. Next slow cooking dishes will be done (rice, beans, roasts).
3. Depending of the side dishes these will be prepared next, and may be cooked at the last moment before serving.
4. The last thing to be done will be the starters - actually the first thing to be served.
Likewise with piano teaching. Reading music is going to take a while, so it must be started at the first lesson, and "cook" for a couple of months before it can be of any use.
Meanwhile, you must teach some music by rote, otherwise even the most motivated student will despair.
Scales should also be taught (in very small doses – which will add up in the course of time) from the first lesson since it will be a while (sometimes a long while) before they start to make sense.
Technique is immediate. Anything the student does will need technical supervision and guidance straight away.
You get the idea.
By doing everything at the same time, and yet allowing each component of the whole its proper completion time, you should have a beautiful flowering of skills after two three months, when everything comes together.
Likewise in the kitchen, by taking into consideration each dish's requirement in terms of cooking time, you should be able to have a beautiful meal coming together perfectly timed at the end of a couple of hours.
But it will not happen at first. Set your sights on that goal, though, and soon you will get the hang of it.
Here are three helpful references:
James Bastien - How to teach piano successfully - Kjos
Dennis Agay - Teaching piano (2 vols.) - Yorktown Music Press.
Uzsler, Gordon & McBride Smith - The well tempered keyboard teacher – Wadsworth.
And if you do not know this book, you will like it:
Eigedinger – Chopin, pianist and teacher – Cambridge.
Chopin had been working on a teaching method before his death, so he never completed it, but his book has the unfinished version. Enjoy!
Best wishes,
Bernhard.