Before you start consider this. What happens if the electronic door lock fails? If you use fail secure you get locked out, if you use fail safe you let unwanted visitors into your house. A project for an electronics starter? I think not. Not if you want to employ a locksmith, only to stand outside for hours to wait for them, or want the unwanted visitors into your house and take all of the things.
Gather basic knowledge of electronics, start out with some simple projects. Make things. When you become advanced this, in my opinion, is a valid project. It is just that if ONE wire/component slips out of place your system is likely to be useless.
If you want my opinion on the shop selection, Maplin will sell you all the things I can think of that you would need for your door lock. Integrated circuits, voltage regulators, capacitors, resistors and so on and so on.
I hope this helps,