If you are planning to run only one engine in steam (one train working, nowadays) then you could get away with no signals but you would be restricted to having one train arriving, dealing with it's train and then departing before another could arrive.
Imagining your railway is worked by train staff and ticket or electric token, allowing more than one train in the station at the same time, then you would most likely need them.
The least you could get away with would probably be a home (or arrival) signal protecting the station from the incoming single line though a starting (or departure) signal would most probably be insisted upon by the HMRI as well.
The Talyllyn Railway manages to cross trains at Brynglas and Quarry Siding using only flag signals though the points are worked from ground frames in cabins.
A signal box would not be needed, you could have a ground frame controlling the signals and the connection from the loop to the main line. Hand levers would control the other points. The token instrument would be assumed to be in the station office.