About to start a new project

Alright ive been getting back into modeling. I really want to customize the model this time. i was wondering if the Tamiya Polyester putty (http://www.hlj.com/cgi-perl/hljpage.cgi?TAM87027) was any good and about how much work could i do with it. I'm looking for something that has enough for a body kit and something that is a good starting putty. Also im looking at getting a nissan silvia s15 model. I found the Fujimi one and i have always been babied with Tamiya models. How big of a difference are the two. thanks.

You seem to have two issues:

Tamiya vs. Fujimi and How to build up bodykits

Tamiya vs. Fujimi
Fujimi kits are usually more simplified than Tamiya kits, but at the same time, they often have errors or flaws, either in accuracy or in engineering. Sometimes details will be wrong for a particular car, and sometimes parts won't fit well...

You'd have to pick out a particular kit, and people on the board that have said kit could tell you the pros and cons about it.

How to build up bodykits
You will be 1000% better off if you can make some kind of skeleton for your additions, then use putty on top of that to form the final shape. Many hobby stores sell styrene plastic stock in sheets and strips which you can cut and form into the basic shapes you want. flyonthewall has made some remarkable posts on the topic, if you care to go looking.

Both polyester and epoxy putties are suitable for body-shaping work, as neither shrinks while curing, but I think the "frame" concept is more important than which type of putty to use...