Yes, increase on what you have as corys are shoaling fish and prefer the company of their own kind.
I would avoid panda corys - they are very fragile and don't last very long - plus they are so small they are barely seen in an aquarium with lots of rocks/plants/caves etc.
I made the mistake of buying 4 recently - bought them on a spur of moment decision instead of getting what I'd gone in there for (more Sterbai). Expensive mistake on my part! Started reading up on them when I got the first available chance after that weekend, only to find lots of negative feedback on them (despite them being cute little guys the general consensus was that they are quite weak fish and perish easily). Also I discovered they need lower tank temp (mine is at 28 degrees).
So, of course, within a couple of days all but one had died!
I gradually lowered the temp down over a few days but who knows if the last little chap will survive. He's probably really lonely now...
Athena