The CI-V protocol requires that you be able to read and write a serial character at the same time because CI-V requires that when you write a byte, you also read it back to make sure it is what you sent (the CI-V hardware "reflects" the Tx back into the Rx). When you use softwareserial you can't read a character while you are writing one.
You could use the Arduino's hardware Serial port on pins 0 and 1 but that makes development/debugging difficult.
It's much easier if you have an Arduino which has at least two hardware serial ports. You can then have program uploading done on the Serial port as usual, and have the CI-V bus connected to Serial1.
If you have a Teensy, it is even easier because Teensys use native USB to upload code (i.e. they don't use the Serial port to upload) so you can get away with, for example a Teensy2 which has one Serial port and use that for the CI-V bus.
how do you turn on civ transcieve mode
what baud rate does it work on?
See pages 46 and 47 in the manual. You can choose whatever baud rate you like. Start with 9600 and if that seems to be too slow, bump it up to 19200 or even higher - if the rig can go higher.
Pete