Yes, if you make the water too acidic, you can kill your plants. Just do a 1 or 1.5 degree pH drop. So measure pH when tank is completely off gassed, then measure pH after several hours of CO2 injection. Plant a lot of DHG off the get go. It can be demanding, sounds like you've got all the ingredients for success. Also, start with no more than 5 hours at 100% strength light until you have some plant mass built up, then you can start ramping up time slowly at that point.
Do not inject CO2 directly into your filter, air hitting the impeller constantly isn't good. Get yourself a 3 pack of in-tank glass diffusers. They'll need frequent bleach baths to keep pores clean so that's why the 3 pack is nice.
To achieve growth, you need micros and macros, so NPK are your macros, CSM+B or Miller's Complex for your micro mix. Good light and adequate CO2 with that and you're golden. Be patient. Don't ramp that light up past 5 hours until there's plenty of mass and if you start seeing algae, go down to 4 hours. 50% weekly water changes if you're dosing EI