These should work on most DMPs especially EPSON ones.
Basically there are 3 font sizes built into the printer firmware.

1) Normal size

2) Large size – Use chr(14)

Eg; Print #1, chr(14); “ABCDE”

Will print ABCDE in large sized font. To revert back to normal size you can use chr(18)

Eg; Print #1, chr(14); “ABCDE”; chr(18); “XYZ”

Will print ABCDE in large sized font and XYZ in normal sized font.

3) Condensed – Use chr(15)

Eg; Print #1, chr(15); “ABCDE”

Will print ABCDE in condensed font. To revert back to normal size you can use chr(18)

Eg; Print #1, chr(15); “ABCDE”; chr(18); “XYZ”

Will print ABCDE in condensed font and XYZ in normal sized font.

This is all that I know.

Regarding pagesize, there are specific codes. These may be found in the Printer manual.

As far as I am concerned, in the progrmme I count the number of lines and send a page eject (chr(12)) when required. For example if the length of paper is 12″ and you are printing @ 6 lines per inch with 1″ margin on top and bottom, you can print 60 line on a sheet. After 60 lines you give a page eject to start the new page.

1. How can i give blank line between lines ? (IF i need one blank line)

Print #1, vbnewline

2. Suppose my paper width is 9 inches, How many characters to be printed in one line ? (horizontal line)

Depends on the font size. Normally it is 10 cpi. So after leaving 1 inch margin on left and right it will be 7*10 = 70 characters.