Well if you want a tropical epic full community, you could go with
1- angel fish
1 pictus catfish
6 Julii corydoas catfish or kuhli loaches
6- schooling fish
6- schooling fish
3 platys or mollies
3 guppies
Now for the schooling fish, you can either get 1 Schoo of 12 or pick 2 of 6. Some of those fish could be... Cherry barbs, black phantom tetras, zebra danios, harqualine rasboras, bleading heart tetras, golden barbs, cardnil tetras, and neon tetras.
Senegal bichir's are predatory fish. They will eat any fish they can fit in their mouth. It can grow to 12". I will post a list of possible suitable tank mates but the ghost shrimp will eventually be snacks and I honestly don't know about the crabs. From the list below a school of Red-linned torpedo barb-Puntius denisonii would be a good choice as they are striking fish.
Here is a list of possible tankmates for a senegal bircher and many grow too large for a 55g.
CATFISH
Dusky Pimelodid-Pimelodus blochii
Giraffe Catfish-Auchenoglanis occidentalis
Dwarf giraffe Catfish-Parauchenoglanis macrostoma
Giant Whiptail Catfish-Sturisoma aureum
Synodontis alberti
Synodontis angelicus
Synodontis pleurops
Synodontis decorus
Synodontis eupterus
Synodontis notatus
Synodontis brichardi
Synodontis nigrita
Synodontis flavitaeniata
Synodontis soloni
Liver Catfish-Heteropneustes fossilis
Black Lancer-Bagrichthys hypselopterus
PLECOS
Bristlenose-Ancistrus dolichopterus
CHARACINS
Silver dollar-Metynnis argenteus
Distichodus notospilus-Distichodus notospilus
Congo tetra-Phenacogrammus interruptus
Black-Barred Myleus-Myleus schomburgki
Filament tetra-Bryconaethiop microstoma
EELS
Peacock Eel- Macrognathus aculeatus
CICHLIDS *(see note)
Dicus-Symphysodon discus
Angelfish-Pterophyllum ssp.
Two-Spot Cichlid-Cichlasoma bimaculatum
Tilapia joka-Tilapia joka
Oscar-Astronotus ocellatus
Severum-Cichlasoma severum
Kribensis- Pelvicachromis pulcher
Sparkling Earth Eater-Satanoperca acuticeps
Blue acara-Aequidens pulchrus
Balzani's Earth Eater-Gymnogeophagus balzanii
Blood Parrot Cichlid-Hybrid no scientifc name
Blue-Eye Cichlid-Cichlasoma spilurum
Festivum-Mesonauta festivus
African Peacock Cichlid-Aulonocara nyassae
Balzani's Earth Eater-Gymnogeophagus balzanii
Bandit Cichlid-Aequidens geayi
Blockhead Cichlid-Steatocranus casuarius
Callolepis Cichlid-Cichlasoma callolepis
Freiberg's Peacock Cichlid-Aulonocara jacobfreibergi
Keyhole Cichlid-Cleithracara maronii
Port Acara-Aequidens portalegrensis
Uaru- Uaru amphicanthiodes
LABYRINTH FISHES
Ctenopoma .acutirostre-Ctenopoma .acutirostre
Ctenopoma oxyrhynchus-Ctenopoma oxyrhynchus
Ctenopoma kingsleyae-Ctenopoma kingsleyae
CYPRINIDS
Variegated Shark-Labeo variegatus
Bala Shark-Balantiocheilos melanopterus
Red-Finned Cigar Shark-Leptobarbus hoevenii
Red-linned torpedo barb-Puntius denisonii
Tinfoil Barb-Barbodes schwanefeldii
Chinese Algae Eater-Gyrinocheilus aymonieri
Clown Loach-Botia macracantha
MISC.
African mudfish-Phractolaemus ansorgei
Black Ghost Knifefish -Apteronotus albifrons
Elephantnose-Gnathonemus petersii
African butterfly--Pantondon bucholzi
African Knifefish-Xenomystus nigri