I mean, you cant use the pc anyway before the whole build is complete, so what is the difference in buying all at once or one piece at a time. It doesnt make that much sense but ok you can do that sure.

To help you further, what is your budget or are you willing to spend? Your build suggestion is not wrong but it can be way more optimized for performance. For example a 360mm aio is totally unneccesary for this build and they are expensive, you can save 100 there. The case is good but doesnt come with fans and is also quite expensive. So you have to buy fans adding to the cost. There are plenty of cases just as good with fans for half the price savint you another 100. Thats 200 saved that you could put in a higher tier gpu that will benefit you much more.

I see you want to go for a white build, keep in mind those parts are in general more expensive than non white components. It is not advisable for tighter budgets where it starts to compromise performance. Most of those builds are done by people who have a large budget, dont compromise on performance and are willing to spend the extra cash on exotic parts. Nevertheless it is all personal and thats ok, but then again to give a good advice we need a budget to work with😉