no offense, but there arent many races that you need a viper for...until of course you win the Oreca...
ok, heres some advice...dont waste your money on worthless cars...yeah, you can use the R34 for stuff, or a viper, or whatever...but no.
I like the altezza suggestion...take your lexus to get the LM Race Car. Dont worry about having beginner half answered, you can always go back and do it later...just do whatever you can when you can. The Altezza LM is a good car, and you should be able to use it to take the first few in amateur...which get some mighty fine cars...heres what you can win (using the trick where you save the game before the last race, and win the first 4 so yo ucan skip the last one...)
Japanese Championship - not really worth it...a little bit of money, and its pretty easy, but all you can win is stuff you pretty much already have
American Championship - Good money, can be a challenege if your car is underpowered, but its worth it. Best car, Camaro LM Race Car...thats a nice car, faster than the Altezza, can do some nice stuff with this one...the other cars are pretty boring...
European Championship - This one is harder than the American, best to use the Camaro to do this one...I like this one, the courses are more fun than the others, you get some good prize money, and then the best prize car - the Vertigo. Major fun car...very fast, very fun, very cool...
GT World Championship - This is the hardest of the 5...but the most rewarding...if you have a good car, and you can handle it, its worth it. The Z Concept and the RX-8 are prize cars, and fun, but not worth your time. Instead, you can get the C-West Razo Silvia (dont, its not worth it either) or.....and heres what your baby should be...the GT-One Road Car. Very very good car. Fastest of the bunch, one of my personal favs, great to take out stuff like enduros and other races. Get here soon, and youll be rich...
German Touring Car Championship - this ones kinda hard, but fun and kinda rewarding. You need a pretty good car, but if you have one its a nice simple, fun win. Dont bother with the cup cars, but the Astra Touring car is about as good as the Camaro, maybe a little better, and the RUF is cool but not very practical.
Heres what I did and worked great for me - just use one car to win the next, and then tune it with your prize money and use it to win the next. Get the altezza, then do the races in this order...American, use the Camaro for the Euro and German, you dont really use the astra but its fun to have, but use the Vertigo...I like the vertigo...and use it to take the GT World. It can be a challenging race, but the competition pits + you dont = you win the GT-One. Once oyu have the GT-One, you can do all sorts of things...MRs in pro, Enduros, finish up all those loose ends that you couldnt take before...and, you should be a rich rich man...especially if you do somthing like this...once you get the camaro LM, use it to take the american champ a few times, win more camaros, sell them, and youll have a bunch of money that you can then use for other things like tuning your beetle, 80s, whatever you want. Or get the vertigo, and use that to win more vertigos...they sell for 300,000 each, and the races are more fun than the Amercian champ. You can easily get a few million this way, buy anything you need, and have a whole lot of fun in the mean time.
Heres one last tip - the higher difficulty the race is, the better the prize. So, if you can take the harder races, do it, get the big prizes, and then go back and use your prizes to take the races from before. Makes it alot easier. Or, if you like a challenge (I know some people who do) you can pourposfully limit what you put into your car...but its still nice to have money!
Hope this helps you out, and remember...GT-One is your key to easy enduros...F1 cars...everyone needs F1 cars...