Betta space

All this talk of Betta females has me considering a buddy or 2 for my lone
male Betta. He seems very peaceful, as I've never seen him flare. But he's
only in a 10 gallon tank, so I'm concerned that it would not be enough space
for the three of them.

Should I put a divider in the tank and see how he reacts to the two females
before letting them interact? He's been in the tank about six months now, so
he likely considers it his personal space. Should I add both females at the
same time or space them out? Any preference for the colours of the females
(male is Indigo with red highlights) in terms of compatibility?