...lots of good advice already, Eric-M6, but you've put quite a lot of pressure on yourself by promising a poster. Let's hope that doesn't prevent you having fun
My best advice would be to hire a professional/commercial photographer for the day as your "assistant" - if you can afford it
I'm not being flippant: you'll be guaranteed to get the shots you want, the day will be enjoyable viz-a-viz stressful - and you'll learn a lot
Other than that, i'm happy to offer the following suggestions/advice (although you should note i am not a motoring journalist/photographer)
What you propose is technically challenging...
* Do some research:
(i) visit your library - rent some motoring publications and glossy magazines containing advertisements for vehicles. This will give you some ideas for composition
(ii) take careful note of parked vehicles where you live, especially new or polished ones. Look at how the panels and chrome mirror their surroundings and the sun; figure out how you might avoid that from ruining your shots (refer to the magazines for visual clues)
(iii) Decide on what film you are going to use, then shoot and develop/print a roll of each to test your exposure and settings
Remember - "film is cheap, but moments are precious" (an old Russian photographer taught me that) ... you may not have this opportunity again
(iv) previsualise the shots you want to take: make up a story board or a scrap book from the magazines and take it with you
* Choice of vehicle:
Grey/silver - preferably with a matte or metallic finish to diminish the mirroring affect of surrounding objects
(i) Don't get fancy, this is not a time to experiment - use what you are familiar with - or test (as suggested) my personal choices for this job, which would be:
(ii) Kodak T-Max 100 (B&W) / FUJICHROME Velvia 50 (colour transparency) / FUJIFILM Reala 100 (colour negative) / ILFORD XP-II Super 400 (B&W, C-41 process)
(iii) Take 10 - 12 rolls, minimum
(i) Camera tripod for the slow film and low light situations (morning and afternoon will provide the best lighting for this work)
(ii) shutter release cable for slow shutter speeds/long exposures
(iii) a hand held light meter for accurate exposures
(iv) lens selection: from 18mm through to 300mm if you have them, primes or zooms
(v) materials to clean off road grime and polish vehicle before each shot
(i) unless you are experienced with flash - leave it out. This will only add unnecessary technical challenges
(ii) shoot to your scrap book/story board (as above) but also experiment - especially with the wide angles up close & low, the mid range for isolated trim or detail on vehicle and long range to foreshorten the subject
(iii) for good depth of field and retaining entire subject in focus - shoot with your apertures shut down, + 1 to 2 stops from minimum (tripod?) or use the 'depth of field preview' function if available
(iv) don't meter off subject if using TTL, the car will likely fool your meter. Use a hand held for ambient reading - or TTL meter off the ground
(v) try to record what your settings are for each shot: use this as a reference when prints come back and study the results - you will learn much from this!
(vi) Reconsider your decision not to hire a professional "assistant"
* Most Importantly...
... and now - what about those beers, MD?