My first betta was kept in an artificially planted tank (silk plants) and while he was active and seemingly healthy his colours and overall behaviour improved substantially once he was moved into an aquarium with live plants. I started seeing more natural behaviours (such as hunting through the plants for microorganisms) as well which was wonderful.
I started with sand substrate too and found no issues with keeping plants alive; ferts certainly help but I didn't use them back when I first had live plants and still had good growth rates. I use ferts now in my heavily planted tank and definitely recommend them but you need to make sure you get the right one for your purpose; check dosages carefully as too much can cause an algae bloom.
I use an aquarium LED grow light for my tanks and as long as I have lots of floating plants I have had no issues with my bettas finding it offensive; duckweed is amazing in that respect as it's small and very dainty, beautiful to look at -- if you find it starts to take over, however, make sure you compost it -- don't flush it as it's a pest and can take over local waterways.
Your tank looks lovely so far