Regarding the torrents, yes you can point the new torrents to the old folders and have it "check" the files. I just did this yesterday. You probably have to rename the folder before-hand to match the new torrent folder name. That's what I did, anyway.
No, you can't keep your mame.ini from the earlier version. Sorry.
But what you can do is use a comparison/diff tool like
BeyondCompare to examine the files side-by-side and move your changes over to the new file.