What to use with your soap is up to you. Where and how you store your soap is really the important factor. Keeping your soap dry in-between uses will prolong the life. I suggest using a well draining soap dish like this one I found for $.99.
If you have it on your counters, you can put it in a pretty soap dish to keep the water off your counter. Don't store your soap under your shower head, but instead keep it away from possible drips and puddles.
On average, fully cured handmade soaps should last 1 week per ounce. This is for one person, so if you are sharing this will be less time.