I left LW running 24 hrs or near to it for 3 days over the first two weeks of this month. That's used up 2/3 of my peak hours usage. lol So I am going to be restricting my peak hour usage until next month & instead mostly only using LW during off-peak hours (which has 60% higher bandwidth usage total); 25/40 MB/mth peak & off peak plan. I upload at anywhere up to 95 KB/s. Downloads much faster. I share all types of files including videos.
Good question about how to monitor how much you use. I check my ISP daily & monthly totals.
Whilst you say you only share music, sometimes people download files very quickly from you & it's not easy to see how many files have been uploaded unless you have LW set to not clear uploads. I have it set to clear so they don't clog up the window lol. If you click on each of your shared folders in your Library window, it will show a column beside the shared files which shows upload totals for each file.
LW changed their options. They did have a Statistics option to show all total uploads, etc. They do now have a Logging window which shows what people have done, such as browsing you, selected to download files from you, etc. This window can be found via View options.
I haven't checked these options in such a long time. I will ask some others about it.