Whichever you prefer--bettas will adapt to higher flow just fine.
Was this a live coral that has died? If so...I'd prefer to remove it, since it will decay and contribute to ammonia levels above what the bacteria can
I am looking to buy some Cyprichromis and shelldwellers to go into my 75 gallon(and eventually my 210 if needed). I live in Oklahoma,
Looks very nice! Once those plants get larger i bet your angel will be even happier and play in the plants. I like kuhli loaches and was gonna buy some
The higher oxygen levels can be achieved by adding an airstone. I have 2 planted tanks and even though theyre very nice looking IMO id say try a hardscape