@Neilla If you give more info, we can perhaps make some suggestions.

@CVVT Some models of Deco are compatible with EasyMesh, hence could make a single mesh with the HX220. See more info in https://community.tp-link.com/en/home/forum/topic/710684.

@CVVT Does the ISP router replace something else? The ISP router will not be "in" the mesh. It will be used by the mesh to access Internet. I suggest running the Deco mesh in "Access Point" mode, and...

@rabers Yes, this will work, if the Deco is compatible why your ISP.

@MatteoV What are the max dimensions?

@Nazham95 I believe the X10 will mainly improve the coverage provided by the repeaters. The X10 is quite similar to the C7. I would rather look into the X50, or a mix of X50 and X10.