I don't think you necessarily need a heater, depending on the air temps in your room.
My Bio Orb (years and years ago) didn't have a strong current. You can always not use the filtration they have and add in a sponge filter. Great for shrimp tanks, as they're safe for baby shrimp and shrimp feed on the material that collects on the outside of the sponge.
Agreed, live plants would be very much appreciated by the shrimp. The plants will provide a home for many small organisms that the shrimp will feed on.
RCS do best in low to mid 70s. A heater won't help keep it at 74 F if the room temp is 78 F, so a heater won't solve your problems in this case.I disagree with not needing a heater. Room temperature fluctuations and all that.