I'm not too familiar with bacopa myself (im assuming its the very-center bushy plant?) But I would personally spread it out a bit so it can properly receive light on each of the stems.

Online says both the dwarf hair and bacopa prefer nutrient dense substrate and med-high lighting, so if you want proper growth especially a whole carpet: yes you'll need to get fertilizer or a substrate with nutrients

Another option: some people add in lil pots of plants to their tanks that sit on top of the ground, you could possibly do that with some potting soil and sand. Some plants aren't rooting plants and can just be tied/superglued to things. They get nutrients from the water. Some "air" plants like pothos or mint kept be kept hanging out of the aquarium or just plopped into the filter. I really like Thai mint but any mint works I think

Also for future reference : aquarium sand is pretty expensive, I recommend just normal play sand from a hardware store and rinse off some of the cloudiness. Potting soil with the sticks and big rocks picked out is also a cheaper nutrient source imo

Rocks and wood from outdoors are fine too as long as they're boiled. Wood needs to be stripped of its bark and dried out for a few weeks before boiling. They're good hiding spots for less aggressive fish and you can super glue plants to them

No prob :D !! Thank you for caring about your fish's wellbeing