Absolutely. Add as many plants as you like. The more, the merrier. And don't feel bad if you start having any problems with plants. I am indeed an algae grower at this stage myself. It takes a bit of time to learn how to get everything adjusted.
I can now personally recognize fuzzy algae, black beard algae, hair algae, and my latest addition is staghorn algae!
And I'm also learning which plants can't take Excel the hard way. Here's my method:
(1) Buy plant.
(2) Read that plant will melt with Excel.
(4) Buy another plant.
(5) Read that plant will melt with Excel.
(6) Moan again.
(7) Ask which plants melt with Excel.
(8) Get list that tells me I'm finally safe to get more plants.
(9) Find out Excel is not good for my shrimp.
The point being, it's a learning process. It's all part of the fun, though. So when pin holes start showing up in your leaves or your water suddenly turns green, don't worry. You're in good company.