The first thing I suggest you do is get the pump running and run a hose to discharge and see if you can get the pressure to hold steady at a pressure just below shutoff. Then measure the flow rate with a bucket and a watch.
If your water pressure gauge seems erratic, you should replace it.
With that information, you can determine how many gallons per minute you will be able to deliver to your garden. You will also be able to determine how your tank will work and what Cycle Stop Valve you might want to use.
The pump is not a Franklin pump. The motor is a Franklin motor. Franklin makes motors for submersible pumps. If you have a control box with a Franklin label, with 3 wires, with or without a ground to the pump, then you have a 3-wire pump. That doesn't matter for the moment but there will be a time that it will matter.
Nine gallons drawdown (water delivered from pump shutoff to pump start) is about right for a WX 203 with 30 to 50 psi settings. That it probably on the small size for your pump. How long does it take to pump from start to stop if you aren't using water? It should be at least a minute. If much less than a minute, you should have a larger tank, unless you add a Cycle Stop Valve or a Smart Tee that someone else will explain.
A tank should not contain a lot of water. You can check the air pressure in the tank as follows.
1. At about 35 psi water pressure, measure the air pressure in the tank with a tire gauge and compare it to the water pressure gauge. They should be the same. If the air pressure is different, remember the difference. You will use it in the next step.
2. With the power off, drain all of the water from the tank. Then, measure the air pressure again. You want the air pressure to be about 2 psi below the switch start pressure, so about 28 psi for a 30 psi start. Now for that previous air pressure measurement; if the air pressure was 2 psi below the water pressure, then set the air pressure at 26 to compensate. If the air pressure was 3 psi higher than the water pressure, then set the air pressure for the empty tank at 28+3=31 psi.