Tad is right that a good flush is the way to begin. Ensure that your vent hose to the holding tank is not plugged (spiders, dust, etc.). Wipe each of your hoses with a hot damp cloth, and if the cloth smells it suggests that your hoses are no longer functional and need to be replaced as Tad recommended. Ensure that your hose clamps are tight and there is no leakage anywhere. Flush the head thoroughly so everything goes through to the holding tank rather than sit in the hose for any length of time.
There are products you can buy at chandleries to help decompose in the holding tank and help with odors. There is also a spray called something like No Odor that does a good job of dispelling odours for a limited time.
Also check your bilge to ensure that it is clean, as they can contribute to musty smell. And if you have any mildew in the boat (lockers, cushions, etc.) you will need to get rid of it.
Finally, open hatches whenever you can to get air flow through the boat.
As for the relaxation part, once you get used to the boat and more comfortable sailing her, it will become second nature. Few things are more relaxing at that point!
Good luck!
Frank