I was there for Mardi Gras this year in February and March.
The parade was every night, a change from past years. They were also allowing annual pass members to ride on the floats. I really wanted to do it, but it never worked out.
February was amazing, no waits, no crowds, front row for the parade, plenty of beads. The parks were pretty dead.
March was beyond crowded. Long lines. Huge parade crowd, very lively. Still got a few beads, but you'd definitely want to stake out a parade spot in advance. Same with riding on the float. In February plenty of last minute spots, but in March, it was very booked up.
The concerts were Friday, Saturday, Sunday, and only access to Universal where they are held was blocked. IOA was still accessible.
Keep in mind, you also loose access to the Hogwarts Express on concert days since you can't hop. There were a few people upset because they didn't understand why they couldn't just ride it over and straight back, but they won't let you do that.
What I did to get around the blackout issue this past spring was to buy regular tickets, making sure they cost less than a season pass would. Then on the last day of the trip, we upgraded to a season pass inside the park.
This allowed us to enter Universal on concert days using a regular non blacked out ticket. Then on our last day of the standard ticket, second to last of the trip, which I think was another concert day, we again entered on the regular ticket, went to guest services inside the park, and updated to the season pass. As long as we didn't leave Universal, we were ok, as the season passes wouldn't have let those in our group re-enter on a concert night. Hope that makes sense. Maybe that option could work for you if you haven't already bought tickets.