I am slowly building my own race team in B-Spec.
I HAD two B-Spec racers, but I had to retire one of them. My former second B-Spec racer, Y.Sugimoto (whom I've named Yuji Sugimoto) lost two straight races that he could have easily won. They were his first two races as I tried to give him some experience. This [AI] dope not only spins out in the first corner at Autumn Ring Mini, but stopped on the road to let other cars pass instead of get back on the attack. After two straight 8th Place finishes in the at Autumn Ring Mini, I HAD to retire him.
My new driver, J.George (whom I've named Jeff George), won his first races at Sunday Cup in my Race Modified Nissan Silvia. I then challenged him to take on the FR Challenge at Grand Valley East, and he won that. Two podium finishes at Tsukuba was good for him, but one he just let his guard down and lost on the final lap at Tsukuba. Jeff won at the FR Challenge Trial Mountain stage. Typing this up, I put Jeff in the Yaris Race at Tsukuba, and my mostly unmodified Yaris
Something you have to keep in mind is that if you haven't raced in a certain event in B-Spec yet/A-Spec, but cleared it in A-Spec/B-Spec; try to hold onto that car so you can use it in the other race. I'd only go for a new car, or upgrade the current one, only if you need to. If the car you use worked for you, it may work for your B-Spec racer as well. Overall, I think this B-Spec setup is much better than GT5 because it really seems like you are your own Team Principal or Crew Chief rather than an AI racer taking over in your place.
Besides B-Spec, I've entered into the Professional Series and won the Mini Challenge A-Spec event last night. Being the GT veteran of 10+ years, I'm very sure the races will get much tougher by this point. I already have two proud stallions for when I get to the [sadly abbreviated] Gran Turismo World Championship.