RV/Camper Discussion would do nicely.
The tank is pretty big. I think it is around 40 or 45 gallons but I can't swear to it. Depends on how many people are using the water. I would say that with four people it should last through a weekend or so.
The fridge doesn't use a whole lot of propane so it shouldn't be a problem. Make sure both tanks are full and, if you have a gauge, check it to see how much it uses in a day's time. I'm sure it won't be much.
Put it this way, both our tanks were filled up last July. Since that time, we have run the fridge for a short time coming and going to our destinations. We always use the stove top and the hot water heater and take showers in the camper about half the time (5 of us.) We have also used the furnace for 8 days total during the cooler seasons. After all of this, one tank was empty on our last trip out in April. We're running on the second tank now and it is still pretty much full. So, none of it uses much propane. I would think that it wouldn't be a problem for you.
About possible leaks...we had a small leak in a pipe right around the hot water heater under the sink. It was just a very small drip. We didn't notice it until we winterized the camper this past year. I would suspect it's just air in the lines (it's so easy to get air in the lines) but it's definitely worth looking over just to be sure. A lot of times, we will hook up to the water and turn on the faucets to get the air out but I wouldn't recommend that when you're boon docking because your grey tank will fill up quickly.