Final wav creation. Publishing music to web page. MP3 export settings

I have always had some general questions about how professionals export the final audio from sonar and also what format to export the MP3 for use on a web page.   
 
To create a wav to send to mastering service I selected all, exported to BUS, selected only the "master" bus.  Is that what we are supposed to do?
 
Also I exported to MP3  (I bought the MP3 add on or whatever from cakewalk).  I used 128 and slide the slider over the far left for highest quality.    That mp3 is on a web page.  I am noticing that there are some artifacts and some small areas that seem to speed up or little low quality areas and its seems to be random depending on which computer, browser or internet connection the computer is using.  Now I did not click that variable rate thing.  
 
How do "professionals" get ready to send to master wavs and ready to publish (premastered) MP3 for website out of sonar platinum?
 
The topic of getting audio setup for a web page can become very big, I just want to to know for sure I am doing things correctly.  As a third , side question.  How do professionals convert music for use on a web page or mobile device? the same MP3 lame encoder we all use?