I'm pretty sure that our very first car will be bought from the UCD, and more specifically, we'll have the choice between the Toyota Aqua S, the Mazda Demio XD, and the Honda Fit Hybrid. After that, my next cars will likely depend on the campaign. For example, what prize cars we can/will win from events, missions, and licenses - plus what will be required for certain events.
I think I'll pick the Aqua S as my first car, then I'll save for a Subaru BRZ S '15 for the events that require an FR drivetrain. I'd prefer not waiting for the UCD to keep rotating until I find an affordable, used FR car - especially since I understand that the prices in the UCD/LCD reflect real-world appreciating values.
Then again, I don't mind having one of the same car, as I plan to have at least two of most cars in the game, with one to leave as-stock, and another to modify. So even if I did win a prize car that ends up being eligible for another event, it might not be in a color I want, so I'll simply modify the prize car - including the addition of a livery using a different color/pattern. Meanwhile, I'll buy another one of the same model to leave as-stock, provided that the latter car is in one of my preferred colors.
I certainly plan to buy more of the Toyota Aqua S for the "buy ten of the same car" trophy, especially if that first purchase at the UCD counts. Plus, being a 2011 model, it should be readily available at Brand Central, without otherwise relying on the UCD's rotation. If the price of the Aqua S is the same as it was in GT6, then it should be a very affordable 17.9k credits when bought new.
Of course, I'm not 100% sure if the first purchase counts, so just to be safe regarding the "buy ten of the same car" trophy, I might go with buying ten of the Subaru BRZ S '15, as I'd imagine it'll have a remarkable amount of customization options in GT7, just as it does in real life.
Otherwise, in a good way, I'm very unsure of what my path will be regarding my first ten cars. Perhaps in the journal I plan to write that will chronicle my GT7 journey, I'll eventually list what my first ten cars end up being.