In regards to some parts of your concerns, you can enable such in options.
The search function: LW's menu bar, Tools -> Options -> Search. You can enable Remember my recent searches. You can also set default search type there.

To do specific search type, you can either click the drop down search type option to left of search box, else, under Tools menu choose Advanced Search which will give more search options for that file type. I suspect this is what you were unhappy about missing from LW 4 search abilities.

Unfortunately, there are no old versions available for Windows users. Not for Pro users at least.

Not sure if you are interested in trying, but there is the LW 5.5 Beta just released today which has the AVG anti-virus option to use with it. You will find the Pro Beta option on right-side of your Pro download page at the LW website. More information about changes from 5.4.6 here http://wiki.limewire.org/index.php?title=Changelog