Driving is roughly the same. The FFB is smoother and stronger. It is up to you, but I recommend FFB set to 10 in GT5. Some people like 7, but I personally like a good strong feeling.
If you want to heel toe you will have to right foot brake... unless you want to cross your right foot over/under your left foot and heel toe with your left foot. I am pretty sure you would have to be insane though...
. So, yeah, you will have to right foot brake in order to heel toe.
Here is a guide on heel toe technique.
Take apart your G27 pedals and add a stiffer springs for all pedals. I added a slightly stiffer spring for the gas, a
progressive spring for the clutch and a strong spring for the brake. The brake was about 2-3x as stiff as the original. I also added a small foam insert into the brake pedal to give a more realistic feel. All of this costs less than $10 at your local hobby shop. This gave each pedal a unique feel and vastly improved my driving experience.
I also added a piece of yellow tape to the top of my wheel life in a race car. This helps you maintain the wheel's orientation during frantic moments.
Finally, take good care of your wheel. After many years my G25 has started to wear pretty bad. Wearing something like driving gloves will vastly improve the life of your wheel.