Kev's proposed spec is above - not quite a stripper, but almost.
I guess I am confused as "No backing out now unless I want to lose my deposit" and then saying you're talking about your finance deposit, which I assume you haven't paid yet as you've not taken delivery does indeed not make any sense
I think it is inevitable that if you plan to get out in 12-18 months you're putting yourself in the worst position. The finance company will want to make money out of you so your settlement figure will be poor and your finding the time period when depreciation will be highest. You don't have to do the math to do the math ;-)
If, as I beleive you've indicated, your other option is a TT-RS, my view would be that you're unlikely to lose more money on a 1M than a TT-RS./ If you're now looking at other, less outright purchase price, cars, then I'm sure you can find something that will cost you less over 12-18 months than a 1M or a TT-RS.