Of course it is. 5 Gallons is enough. . . lol. If you are new to the hobby ask, ask and ask. There is no stupid question in the hobby. Welcome btw! 25 gallons is a real nice pico size imo, you just have limitations on fish and room. .
25 Gallons is good! Just remember though that the more water you have, the easier it is to keep it stable and stability is key to a successful reef tank.