We have six (6) plant we started from seeds and they are doing just fine.

Does anyone have any advice for us as the plants grow bigger?

I had different citrus trees in my yard in South Florida. Basically you want to bring them indoors in the winter so they do not freeze. Water, but don't ovewater. Get some citrus fertilizer and use very sparingly. Lots of direct sun, no shade. Since you live up north, would suggest planting them in pots not too big to drag inside in the wintertime. Don't let the plants out overnight in temps less than 40 degrees to be on the safe side. Enjoy your lemons. They will get big.