It is a really wonderful kit of a supercool car! If you are patient, then you'll find the kit available at decent prices.
Here are some pictures of the ones I've built:
http://smg.photobucket.com/user/ChillyB1/library/Tamiya Alfa-Romeo Giulia GTA?sort=3&page=1
http://smg.photobucket.com/user/ChillyB1/library/Tamiya Alfa-Romeo GTA?sort=3&page=1
That is a really cool diorama and definitely a great way to display that kit. There are great Ferrari 250 kits available now so that AMT kit can be retired (or put out to pasture).
The TS and AS paints are perfectly compatible; however, be aware that some flat paints are very flat and may take vast quantities of clear to try to make a glossy finish. I experienced this with a Tamiya AS gray (can't remember which one) and TS-13. By the time I realized it just wasn't going to work I'd wasted a lot of paint and nearly a whole can of clear.
Here are some I've built:
I'd advise you to avoid the Gunze Sangyo kit. It is one of a very few kits that I've simply tossed in the trash rather than waste more time, effort, and energy trying to build it into a decent model.
I recommend that you order from Hobby Link Japan (http://www.hlj.com/) rather than go through Amazon. They usually have the best price and are so reliable and responsive that you can rest assured that yours will be a hassle-free transaction. I received a package from them yesterday, less than two weeks from order and payment! There aren't any sorts of import duties or other customs fees for shipments to the USA.