@Fabson 

Archer AX23 is not compatible with Deco mesh. You can turn off its WiFi and use it as wired router together with Deco mesh, or research EasyMesh compatible gear from TP-Link that will work with AX23.

If staying with Deco mesh:

You can plug all three Deco to AX23 directly, but they must run in Access Point mode. You can do the switch after you configured first Deco from the set, then the rest will pick on that setting when added to Deco mesh. See Switching a Deco to Access Point (AP) Mode

You can plug TV to spare port of Deco unit. 

Deco M4 will work just fine with internet speeds up to 500Mbps.