Why I'm getting a lot of moire pattern when I rasterize the tone layers
There are couples possibility cause the moire. But first, I would say don't merge down or rasterize the tone layers before you completly finish the page. Actually I don't recommond to rasterize, keep it in vector mode. MS tone is in vector mode, and it makes sure the tone won't cuz any moire pattern. But when you rasterize the layer, it lost that function.
-Don't overlap different tones together, espeically gradation tone/image/ scenery and screen tone together. It's pretty normal to get those moire pattern by overlapping different tones together, even you tone manully with real tone. It's an effect some mangaka use, and they intend to get the moire effect. (I think is 45 degree angle different on each tone when you apply two tones together...with real tone of course. But MS can do the same effect.)
-When the tone is rasterize, it will show some moire pattern when the zoom in size is not "25%, 50%, and 100%" It's nothing wrong with the program. It's the limitation of all the monitor when viewing tone. (When the monitor can't display the tone in certain resolution.) It's only the viewing problem, the printout should be fine. If print at 100% (It need to print at 100% if the page is rasterize, or it will got moire pattern just like Photoshop did.)
Therefore, don't rasterize the tone layer.