Are you into autox or extreme handling? If not, a lot of suspension mods will be unnecessary. I think I speak for most people that put aftermarket springs and struts on when I say, we do that to lower the car and improve the handling. But, its mostly done just to lower the car.
Sounds like you've been doing your homework...thats a good thing. Question: If you did so much research, why are you getting an ebay CAI
DC is an awesome header. Hotshot also makes a header. I bought the Hotshot before DC produced theirs. If I had not, then I would go DC, so good choice on the header.
Springs and struts will all depend on your preference. Just stay with a known name brand an you are ok. I say its based on your preference because it depends on how stiff you want your ride to be and how low oyu want it. IMO, Hotchkis makes the best suspension parts for the celica. I have their springs on my car. If you want to uprade the suspension some more, get a front and rear strut bar and sway bars. That should be all you need to do to your suspension for awesome handling.
As for the pullies. If I had the money, I would buy them. There is a huge controversy on it, and people do sooo much research and bla bla. I have not seen any documentation putting the blame fully on UR, nor have I heard UR say that their pulley MAY have caused the failure.
I think that answered most of you questions