Glad to hear your downloads have started again, or some. I don't know what might cause the freezing. Sounds like either a memory or cpu issue. If you are using Vista or Windows 7, Java should be set to Run as Administrator. This seems to help LW to behave better and connect more easily.

Inconsistent speeds is not necessarily unusual. Particularly if the uploader is also busy uploading to others. But it should not be too jagged in speed.

Try not to download too many files from the one person at one time. The uploader will probably only have a certain number of upload slots set to be available and some might be busy. If you try to download too many files from one person at once, some of your downloads will probably fail as they wait in queue then are unable to get a slot within a period of time. How to know if they are from same person? Right-click each of the files in the search results and check their ip or nickname and see if they are identical. Downloading 1-3 files at once from same person is usually a good and polite approach.
5 Ultrapeers is standard for being in Leaf mode. The original LW Basic only connected to 3 U.P.'s and Pro to 5. Only if you are running as an ultrapeer will you connect to more U.P.'s ... standard when running in U.P. mode is 32 U.P.'s and perhaps 40 Leafs. But you will never obtain that status if your LW says you are behind a firewall.

Chances are your router needs port forwarding. If UPnP is not working, ie: LW communicates with the router and requests a port to be opened temporarily whilst LW is running. Your router may not have UPnP or not very good UPnP, or else, you have not enabled UPnP in your router settings. Some routers/modems have UPnP enabled by default, some you need to manually turn on. If you wanted to solve that side of it, then log into your router and see if there is a UPnP option. It will probably be under the Firewall heading. Otherwise, port forwarding is the alternative.