Is it too early to plan a wedding for 2028?

It certainly doesn't hurt to start looking around to get an idea of what venues you like, ideas for decor, dress styles, etc, but I wouldn't book or buy anything right now, as 3.5 years in advance is a little soon. Many venues and vendors also might not be accepting bookings for 2028 yet. I would wait until around 2 years in advance before signing contracts for anything. A good time to purchase a dress would be around a year in advance (especially if ordering a gown instead of buying one off the rack). Congratulations on your engagement! Happy wedding planning!