To avoid problems, given the mix you have with shark, cichlidd, panchax etc you can't go small really. I don't know what size tank you have now but I wouldn't go smaller than 200litres I don't think.
TROPICAL TANK-Elite Tank - 207litres
6 Harlequin Rasboras, 5 Emerald Eye Rasboras, 10 Cherry Barbs, 2 Bristlenose Plecs, 2 Panda Corys. 4 Dwarf Chain Loaches.
ViaAqua Tank AR620 97litres
1 red male betta, 1 BN