23inch Length + 11inch Width + 14inch Depth.
Ok, about 58 litres or 12 gallons. Sorry to say but the cichlid is still too big to be in there, plus they have very specific requirements that are completely different from that of the betta. If you want to be keeping african cichlids successfully you'll need to be thinking of a much bigger tank (about 55 gal).
However, it IS a great size for a small tropical community, including the betta.
With you betta you need to be careful of aggressive fish and fin nippers, plus your betta's attitude towards other similar-looking fish. That puts guppies out of the equation, although I keep mine successfully with endler's livebearers so that's an option.
Good tankmates in a community tank of this size include:
A small shoal of small, peaceful tetras (ember, neon, perhaps glowlight etc)
Rasboras or microrasboras (chilli, galaxy, harlequin, lambchop)
Platies (although i would say it's too small for swordtails)
Ottos
Cories (probably pygmy would be best)
Kuhli loches might work? I'll leave that one to someone with more experience.
Shrimp can work with a betta, as can snails.
Have a look around the internet and LFS and see what you like, we can help you out as to whether they're suitable