5ppm for nitrate is really low. If you have live plants it could be too low.
One thing to do is make sure you are doing the tests correctly. If you are using test strips then i really wouldn't trust them. If i test my tanks with a test strip it tells me 5ppm nitrate, if i test using a liquid test kit it can be 20 to 40ppm. If you are using an API liquid test kit, really shake bottle #2 as instructed. Like bang it on the countertop. If you don't do this the test will give a falsely low reading. If you have a local fish store that does water testing maybe take a sample of water to them to double check your own test results.
Nitrate is the end product of the nitrogen cycle, and its much less toxic than ammonia or nitrite. For fish, lower is better. 5ppm is better than 10ppm, 10ppm is better than 20ppm etc. Typically 40ppm is where you dont want it go any higher, but if your regular weekly or fortnightly water change keeps it at lower levels that's much better for the fish.
Plants on the other hand need nitrogen. In aquariums they get this from ammonia and nitrate in the water. If nitrate is low then it could cause a nutrient deficiency. You mention getting more live plants, so i presume you already have some. If your plants show signs of nutrient deficiency and your regular water change is keeping nitrate below 10ppm then you may need to use a fertiliser with a good amount of nitrogen in it. Most aquarium fertiliser has practically zero nitrogen as its perceived to cause algae, which it doesnt. It might algae worse, but doesnt cause algae. If you are US based then NA Thrive is a good aquarium fertiliser that will increase nitrate, here in the UK we have TNC complete. Tropica and aquarium coop also do fertiliser with nitrogen/ nitrate in it.
Feed once a day, as much as is eaten in 2 to 3 minutes. If you want to feed more than once a day then dont feed as much as you would with 1 feeding.