رضا: well in all respects رضا those sentences look foreign. I guess IF You had to write it out with the adverb that you chose.. I would say..

1) In what could loosely be called your life, you've made a living watching others.

and

3)In what could be loosely called your life, you've made a living watching others.

but I don't think a scholar would include the word loosely in the sentence.

In what could be called your life, you've made a living watching others.

*~*~*~*~

and in your second example none of the sentences make sense..

He may have gone out. would be the correct way of expressing this..

May and probably are different words, however they are being used the same .. Now.. if you switch and use probably your sentence would look like this..

He probably has gone out.

Hopefully I haven't confused ya..

رضا: we have more words for the same thing and meaning then we need..

"Have to" and "Must" are the same meaning.. they just show the emotion of the user a bit more..

For instance the young child might say to his friend.. "I have to take out the trash before I can go to the movie"..

and The secretary with a dozen letters to type up and send out, while also staring at a report may say something like "I MUST get this report done before noon so that I can finish the letters" in this case.. the "must" is used to emphasize the importance of what is to be done..

I hope this makes sense!

Kewl board by the way.. Good luck with it!