I downloaded ~500Mb of video lectures a day once, 35 Gb of traffic total. And multiple streams were captured simultameously. I had no any problem with that. I watched them, deleted them so there was no illegal distribution and usage.

WM Recorder in the PRO mode and FLV Recorder are very good 'coz even if you generate a large amount of traffic, content provider hardly can suspect anything.

I mean of course one can't watch lectures 24 hours a day. Even multiple students can't do that. But one can have music video streams playing 24/7.

I strongly recommend to use stream recorders as personal archiving tools only. Don't distribute or share your recordings. And read the ToS on the web-site of your content provider. Make sure you don't violate any terms by recording. You should also take into account the laws of the country you reside in.

As for other advices... read other threads to learn more