Can I use Canon 450D for wedding photography? (with 18-55 IS lens kit)

If it's for study, 450D will do. There is no problem in using 18-55 as a beginner. Basic knowledge and composition can be learned, but it is not enough to take wedding photos in the studio.

If the funds are not too abundant, or beginners don't plan to invest too much, it is suggested to consider playing with a fixed focus of 50 1.8 or 50 1.4, which is very convenient for portrait shooting with large aperture or dim light.

I don't recommend Longteng's 17-50. First, the 2.8 aperture of this head is relatively soft, so there are not many opportunities to use it. Secondly, this head is not the whole head, but also the deputy factory, which will lose a lot in the future. If you don't have enough money, use a condom first, and you won't lose anything after you get started.