Does anyone know how busy it will be at the start of May and what rides should be done first. I'm thinking of riding the likes of Silver star, Blue fire and Wodan towards the end of the park days. Also, any good hidden gems that are worth exploring in the park?
No idea how busy it'll be, I'm afraid.
I would recommend getting to Blue Fire and Wodan as early as possible. These tend to be the longest queues in the park and, fortunately for those staying on Resort, are situated right at the back of the park next to the hotel entrance so there will be no queue for them first thing in the morning. Blue Fire it's definitely worth waiting for the front on, for Wodan queue for the back.
Make sure you use early ride time (8:30 - 9:00 for hotel guests) - the ride line-up appears pretty weak but Enzian and Tirol Log Flume are actually two of the most fun rides on-park. Make sure you give the walkthrough outside Enzian's exit a go, too, it really is sublime - full of working animatronics and incredible lighting which make it one of the park's highlights in all honesty.
Silver Star has to towards the end of the day (gives it a chance to warm up and means the queue will be shorter) but don't leave it until right at the end because they close the front row queue and it really is worth the extra wait!
Also, Matterhorn Blitz and Swiss Bob Bahn have poor throughputs so try to get them done early - if you're not hitting Blue Fire and Wodan first thing then these are the ones to head to.
Besides that, have fun and enjoy what is definitely one of the world's best theme parks!