There is a big difference between "Need more sources" and "Awaiting sources"
Need more sources means you need to activate "find more sources" manually Awaiting sources means you SHOULD get connected whan more sources appear. However Limewire is not very good at finding more sources, and it helps to re-search the subject (no need to activate another download), and if a new source turns up in the search LW will be kick started in to continuing the download.
This also can apply to your second question .. Limewire will often connect more hosts automatically but re-rearching can also help
Some uploaders like to see if someone downloading from them is sharing, and if they cannot see that they are, they are might stop the transfer. It is wrong to do this because it is almost impossible to see if someone is actually not sharing or not.... but it does happen.
I really am not too sure if your upload speed and allowance can affect your download speeds.. there are mixed opinions and I'll let someone answer that ......