Since you have a pentagon tank, I'm assuming that it is not as long as a typical 30 gallon tank. Regardless, I would not stock more than one pair of Apistogramma in a 30 gallon. Here's a good example of why.
That's a male Apistogramma borelli. Clearly he is an anomaly, but most Apistos get larger than I think a lot of people realize. The rams in the pics above are pretty, but are also nowhere near max adult size.
I've found that an aquarium looks more put-together with larger numbers of one species of schooling fish vs. multiple groups of smaller numbers. The fish are usually more interesting to observe in larger numbers as well. Pencilfish have never done well for me, unfortunately, but you mentioned rasboras... I'm a big fan of harlequin rasboras for a lot of setups. They're easy to keep, very hardy, and show nice coloration once you've had them a while. You could easily keep 10-12.
Corydoras often make good tank mates, but be sure to research the temp requirements of the species you like- some prefer cooler water than the other fish you want. I'd say 4-5 would be good to start off with. The Apistogramma will stay almost exclusively in the bottom half of the tank, so make sure you don't overcrowd down there.
I usually recommend Apisto cacatuoides for someone new to dwarf cichlids. There are several color variants available, they're hardy and easy to keep, and they breed readily in the home aquarium if you're interested in that. They're a great starter apisto.