Actually since it's been set up since Novemeber, the chances of it being cycled are pretty good, I would...assume. That's like 4 months or so, but you should test the water.
I do 50% changes twice a week (I have a cycled 5 gallon with two bettas).
If it's cycled, keep doing once a week, no less. If it's not cycled, every other day!
Take everything the LFS says with a HUGE grain of salt (lol). Oh god, once a month?? Goodness. It doesn't matter if algae thrives on dirty water, once a month is too little. Live plants will definitely help the water. Try not overfeeding, and try not having the light on too much to prevent more algae. Just clean the algae with a sponge or something, they're not hard.