Doing a seasonal festival lot (or even a non-festival lot using seasonal markers) can be a real challenge. Make sure you test it in all four seasons, and make sure you test every item on the lot. Some things become unusable in snow, but NPC Sims will try to get to it and will route fail, and you'll try to send Sims to it and they'll route fail, too. It's very challenging, and a lot of it is due to that.
Also, you have to worry about if you change an item out in the Common area, and not realize it will conflict with something in one of the seasons. I've had that happen to me before.
Your lot is very pretty right now, and you've done a few things that really intrigued me. (I've never thought of using the heart-shaped rugs to make clovers.) I particularly like how you've decorated the dance/maypole area, and the lavender and pink hearts around the helium balloon area.
I can't wait to see how you'll do it for the other seasons. :)