3. What recovery rate can I expect?

That depends. Among the problems with recovering files on a high-quality, multi-tasking, multi-user operating system like Linux is that you never know when someone wants to write to the disk. So when the operating system is told to delete a file, it assumes that the blocks used by that file are fair game when it wants to allocate space for a new file. (This is a specific example of a general principle for Unix-like systems: the kernel and the associated tools assume that the users aren't idiots.) In general, the more usage your machine gets, the less likely you are to be able to recover files successfully.

Also, disk fragmentation can affect the ease of recovering files. If the partition containing the deleted files is very fragmented, you are unlikely to be able to read a whole file.

If your machine, like mine, is effectively a single-user workstation, and you weren't doing anything disk-intensive at the fatal moment of deleting those files, I would expect a recovery rate in the same ball-park as detailed above. I retrieved nearly 94% of the files (and these were binary files, please note) undamaged. If you get 80% or better, you can feel pretty pleased with yourself, I should think.