In June I bought an REI Novarra Randonee, a touring bike. since then, I'v discovered that the gear range on the low end is not quite low enough to suit me. The bike came with a RD 105 long cage and a freewheel with a high of 28 teeth. I'd like to get a rear cog that goes up to 32, so I know I'll have to change out the RD and the chain. Here are my questions:

1) do I need to change anything else beside the rear derailleur, freewheel, and chain?

2) how do I determine the proper length of the new chain?

Thanks for any advice and observations