Listen to Faster and Chef2sail.
Also, make good electrical and speaker connections, for this you should search sailnet and do as Mainsail recommends.
When I bought the boat we had a car stereo and a 5 disk cd changer in her.
FWIW I didn't mount an antenna externally and find my fm reception to be fine most of the time using a small antenna below decks. Also, we use the iPod inside the radio probably 95% of the time aboard but you know your own usage I'm sure.
Here's what I ended up with
Marine radio mounted below, wired remote to be mounted above (haven't done that yet as I have to order a new navpod) , speakers under the stern seats with heat shrink gel filled connections all around.