It was a slow weekend by the house, so I got the dust out of the PS3 and GT6 and started a new save from scratch.
It's my first time playing it with my G29 wheel (I already tried it on GT5 in the past) and, by the
GT6 Unauthorized Player's Guide suggestion, give the mandatory Honda Fit some more life that I used to (I also decided to "forget" that I had all the Anniversary Edition gift cars on my garage).
So, It's more than capable to do all the Novice class, completely stock. Sure, It'll loose a ton in some straights, but the AI is so slow in some corners you can get away with it. It's also a fun car to drive, as you can easily control the natural understeer with the throttle.
With just some bits of upgrade (exhaust manifold, intake, ECU, SH tires, weight reduction) it can easily beat half the National B class series (Freshman Cup, Clubman Cup, City Trials (Tokyo will need some heavy blocking uphill to the finish line), 5-minute races, FF Challenge and the final championship GT Compact Car), which represents half the stars of the National B class.
By than you will unlock the Junior Kart (getting National B license), that you will use Sunday Kart Junior, the Renault Clio RS by getting all the stars on Novice Class, the Lancia Delta by half the stars in National B. If you go for National A license, you will also get the Honda S2000 and if you go for National B missions, you will get the Mitsubishi Lancer Evo VI Tommi Makinen Edition, which is THE CAR to have, according to the guide. For now will allow you to do the Japanes 90's challenge, and the S2000 the FR challenge.
As I ignored the gift cars, I only had to buy a car for Classic Sports Cars Series.
But definetly the Honda FIT should be your starting car.