Can we assign internal page number by hard coding in html? If not, what is the best way to know which page has which page number when we design our monochrome GUI?

There is a file generated at compile time which is not used by the project, the map file (CompileMe.map for example). This file contains the flash header file number for every file, and the format is meant to be used as an include file in your project. See the "uart protocol" under the "Sending" Jump to specific page" Command" section in your Amulet Compiler Software help documentation.