Hey pieman and welcome.
I don't believe the park is doing reservations this year, and if they are, it probably won't be applicable in April since those are usually low volume times.
As for rides, it's hit and miss. Outlaw run is not plus size friendly, and neither is Time Traveler if I recall. Wildfire has seats with seatbelt extenders if needed, and Thunderation is usually something that people can squeeze into. Powderkeg may be a challenge. All coasters have test seats in front so you can find out if you will fit before getting in line.
I think Fire in the hole, the train, and the flooded mine have zero restrictions though, and if it's warm enough, the water rides!