You're slightly overstocked with what you have now. Corydoras are my second favorite next to bettas! They are so fun to watch! I had to move mine out of my betta tank because Neptune thought nipping at them and stealing their food was great fun :/ Check out http://www.aqadvisor.com
for stocking ideas.
King PK Wasabi; HMPK Frostini; 5 CT Bettas Jewel, Shimmer, Opal, Scarlette (aka Ms. Piggy), Pixie; 1 SD Neptune; 1 HM Gypsy; 1 DTHM Pebbles; 4 Orange Von Rio Flame Tetras, 5 Bleeding Heart Tetras, 4 Harlequin Rasboras, 2 False Julii Corydoras Salt & Pepper, 1 Bristlenose Plecostomus Hoover, 2 Pictus Catfish, 1 Albino Rainbow Shark, 5 Dension Barbs