Lap Counter Project

Hello all,

I am a Slot car racer, and I am building a lap counter for home use for my GCSE electronics project. To help me with researching this project, I would like some info on what the most important aspects are, so if any of you can spare a minute to help, I would appreciate it greatly.
Please number the following aspects 1-12 in order of importance:

1. Ease of portability
2. Ability to count up to set number of race laps and then switch over to count down mode for the race
3. Size/compactness
4. Sound at the end of the race to signal the race is finished
5. To be mains powered
6. To be battery powered
7. Should the counter be a box at the side of the track
8. Should the counter be a bridge type over the track
9. Should the counter be mechanical and then be fixed to the underside of the track
10. Should an Infra Red non-contact sensor be used
11. Should individual lap times be recorded
12. Should the best lap time only be recorded

Please answer and feel free to add any general comments as well.
Thanks!