Speed can be sensed using a hall effect sensor with a magnetic device attached to the front wheel. It will send pulses through a wire and then you will have to calculate speed based on the perimetrer of the wheel (Nº of cycles/perimeter=distance--->distance/time elapsed=speed). At least my old bicycle computer was based in that technology. The other things you are trying to measure I haven't investigated yet, so I can't help you with that. There's a lot of information around the web, for example Application note 3845 from maxim: Designing a bicycle computer... If you don't know much about electronics, as you stated, I suggest you to get some help with that project as the programming and interfacing of components won't be simple and yet, not impossible. What I'm trying to tell you is that the project is simple if you have experience with mcus and devices related to them. May be a well explained reference desing could help you.
I know I haven't answered all your questions, but I hope it can get you started at least deciding the mcu you are going to choose, specially with the App. Note from Maxim..
