How can I see the whole file and also wait for more data to be added to that file?

There is a way better way of achieving this:

less +F <file>

It'll show you the whole file, has the full power of less and will wait for new input. If you want to stop waiting for input, and read a specific part, you can stop it with ^C and resume with F.

The F command is always available in less, if you decide to watch for changes while having a file open in less, hitting F will turn it on. Thanks to hiergiltdiestfu and wildcard for pointing that out.

tail lets you add -n to specify the number of lines to display from the end, which can be used in conjunction with -f. If the argument for -n starts with + that is the count of lines from the beginning (0 and 1 displaying the whole file, 2 indicating skip the first line, as indicated by @Ben). So just do:

tail -f -n +0 filename

If your log files get rotated, you can add --retry (or combine -f and --retry into -F as @Hagen suggested)

Also note that in a graphical terminal, you can use the mouse and PageUp/PageDown to scroll back into the history (assuming your buffer is large enough), this information stays there even if you use Ctrl+C to exit tail. If you use less this is far less convenient and AFAIK you have to use the keyboard for scrolling and I don't know of a means to keep less from deinitialising termcap if you forget to start it with -X.

watch command should do that for you.

You can also try

less +FG 

You will have more options with less command to scroll through your file as you say it's a large file.