Pro won't make any difference at all to what video formats you can view!! That depends on what player you're using & which codecs you have installed. (mp3 is an audio format... not video)

Pro lets you connect to 2 extra uptrapeers, so the potential for better search results is there. You'll also be able to download from a couple of extra hosts - 10 compared to basic's 8 (14 if you have a T3 connection). If you have a slowish connection then Pro's not going to make much of a difference to LW's performance.

I think it's a good idea to get to know the basic version first. Iron out any problems using that & then, if you decide to get Pro later then that's good. Lots of people see buying Pro more as a donation towards the development of LW