If the roots fill the pot then it should be fine.
Fertiliser is a good idea. I don't know what is available where you are as I'm in the UK, but the rule of thumb is 'weakly weekly' to avoid burning the roots. So basically rather than strongly once a month you should fertilise every week using a weak solution.
I believe any Balanced fertiliser can be used, Urea free is best. Ray has a calculator on his website to help calculate a good strenght for weekly fertilisation.
Fertilizer Mixing Calculators
He also has some good info on how to fertilise, take a look at the links here.
First Rays' Free Info