Is my PH too low?

I don't think 6.4 isn't too low. A lot of community fish prefer low pH levels, so unless you're planning on getting African cichlids (for another tank, not your community tank, of course), I wouldn't be too concerned. Your nitrate is borderline high, but I think your plants should take care of that

Try and go for 30ppm nitrates... and then if you get that far, go to 20ppm. It really makes a world of difference in the aquarium and the health of your fish (longterm). At least thats my opinion anyway.

Fully agreed that 6.4 is not too low for your fish,

That being said, You may want to do a KH test. especially if your tank is lower than tap. Things to think about along this line.
If you just started testing PH, it may be that it already dropped due to low kh and it has the potential to continue dropping.

Is you tap water 6.8 right out of the tap or after sitting in a shallow bowl for 24 hours. tap water typically has high levels of Co2 and the ph will raise after the o2/co2 equalize.
Next, if your kh is too low, your Ph can continually drop. this can occur with or without live plants, but is more commonly thought of with plants.

If your kh is kept at or above 4 ppm your ph will stay steady and stable within reason, and this will be better for your fish.

The nitrate levels are higher than I like in my tanks, but not astronomical. my personal goal is to never show nitrates above 20 ppm. I test before water changes to find out what my nitrates have climbed to and adjust maintenance/ feeding to keep them in check.

Plants do reduce nitrates, however don't be lulled into a false sense of security, the nitrate test gives us a general view of water quality, there are many pollutants that we can't test for but go out with the water changes just as nitrates do. When plants consume the nitrates, they leave the other pollutants behind. In a heavily planted tank, frequent water changes are a must because of the things that build up in water that we can't test for. IF you cn find some good articles on OTS (Old tank syndrome) most of these things are discussed at a level above my knowledge or ability to teach. And OTS can effect non-planted tanks as well as planted tanks. I have seen it repeatedly in my brothers tanks, because he does no maintenance or testing. I have seen his ph as low as 5.4 with the same tap water I use. My tanks with a little baking soda added stay steady at 7.6 ph.

A pH of 6.4 Isn't too low, But I Believe That Any lower and biological filtration fails.