What is a good HTML editor other than Notepad?
You can use any editor you are familiar. Notepad++ has a lot of options for representing HTML elements as well as editor functions and more...it's also nice and clean: https://notepad-plus-plus.org/
When there is a large number of Tags specified on one page I do not receive any data.
Use the max_tags_per_msg config parameter as shown in the Programming Reference-HTML5 – Other Configuration Options.
The format of numeric values is showing commas or decimal points and not following the regional language settings.
Use the locale config parameter as shown in the Programming Reference-HTML5 – Other Configuration Options.
What is the client side script to read or write a value?
Use the OPC.get_value(string) or OPC.set_value(string, string) functions as described in Programming Reference-HTML5 – Client Script Library Reference.