There will be replies from folks on this site that are more knowledgeable than I.
But here is my opinion.
For the radiator cap to have failed in that manner the wrong coolant or incompatible coolant was added to the system. Having to add water every other day indicated either a leak ( prior to the water pump leak) or boiling over if you are only using water instead of coolant.
Unfortunately my GUESS is you are looking at replacing the radiator along with the water pump. Then you can do a pressure check for any other leaks.
Prior to this the gasses in the radiator can be tested to see if they are from combustion indicating a head gasket leak, hopefully it is just air being introduced into the system from one of the leaks. The gurgling sound under the dash is likely the air in the coolant going through your heater core.
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