Your comments

When you open an html file, you can choose between code and preview as you can see in the following screenshot:



What exactly is not working for you?

In Textastic 2.2 you can also tap and hold a file in the Files section and choose "Preview" to preview a file using the preview functionality of iOS. This also allows you to preview image, pdf and office files.
You can already search for "\n" (newline) and "\t" (tab). This allows you for example to replace all tabs with spaces or replace one newline with two newline characters.
What's the problem with putting your files into different folders?
I assume you mean something like FireBug?

I'm not sure if this is even possible using the UIWebView that is provided by iOS. Maybe there's a JavaScript debugging library you can include in your website.
What exactly do you mean when you say "buffers"? I'm not familiar with this term in connection with regular expression search.
I plan to show a list of recently opened files when you tap on the file name. This should solve the problem.