transmission<>bittorent

1) no
2) it will not disable it. I think they are using different ports, so you can probably use them next to each other.
3) it is possible. The easiest way is probably to add the torrents to Transmission and download them to the directory where the built-in client downloads to. Unless you really want to keep seeding, you could also just finish the download with the build-in client and add new downloads to transmission
4) in the Frontview menu-> "Add-ons" -> "Installed". It takes a little while to load the list of installed add-ons. Transmission will be one of them and there is a button "Remove"

To use Transmission, you can use the build-in web interface or you can use a program like Transmission Remote dotnet (if you use MS Windows) or Transmission Remote Gui

Had a go at installing it, what's the default username and password ?. (trying to get in to the user interface via firefox)

admin/password1

Moved to Transmission but the web interface runs like a dog.

@dirtydonki, try installing the "transmission remote dotnet" program as discribed above, works fine.

I'm still trying to find where the original bittorent client stored the torents I put in to transfer them to the transmission add on. Anybody know where and how to get at those ?.

I tried the Transmission Remote GUI (Mac OS X) but it failed to connect. It may be due to the ongoing AFP issue. Hopefully the next iteration of this will work.