Dear Sawti,
I think Holi is a good time to celebrate because after that, it'll be months before anything else for employees can be arranged. I believe in keeping it simple where employees gather to enjoy and connect with each other.
So, it can be a small party after 5.00 pm for 2-3 hours, a snacks party where the HR will facilitate everybody with a Gulal tika and a box of sweets. You can choose from varied items for snacks, keeping in mind the background and tastes of the employees. Also, keep some light games to keep them active and the party happening. You can also have a Holi Antakshari Competition and all.
Best of luck,
Paulami Das